The maize quadraplex tetraploids and duplex tetraploids were developed using Kato’s protocols. The phenotype ofheterosis and inbreeding depression over generations in their parents and progenies of F1, F2 and F3 were investigated.The results indicated that different duplex tetraploids have different genetic backgrounds, but they acquire maximumheterosis at same traits, such as the leaf length, leaf width, culm circumference and days to flowering. P.N. rises muchfaster from the F2 to F3 segment than the A.W. does for the plant height in duplex tetraploids. In comparing duplex andquadraplex over a generation the quadriplex is showing the greatest heterosis in plant height, leaf height, leaf width anddays to flowering. Most of the examples achieve the maximum heterosis at Qu F2, with the exception of culm circumference,which achieves greatest heterosis at PNAW F1. Meanwhile, this experiment shows that quadraplex tetraploids has distinctadditional favorable alleles that are not contained in duplex tetraploid, this is demonstrated by the heterosis found incrosses between the two duplex tetraploid. This finding helps explain quadraploids superiority and unique breedingbehavior, in which, the progressive heterosis and inbreeding depression in maize are due mainly to linkage disequilibrium.The severe inbreeding depression in duplex tetraploids is due mainly to the rapid loss of complementary chromosomes orgenes interactions in the first few generation of inbreeding. Correspondingly, the progressive heterosis in quadraplextetraploids is due mainly to a progressive increase in complementarities of homologous chromosomes or genes interactions.Greater complementarities of homologous chromosomes or genes interactions in tetraploids maize alse helps explainrecent molecular biology research indicating that some of traits in quadraplex tetraploids are more responsive to geneticdiversity than in duplex tetraploids. In addition, the dosage effect of polyploid in relation to the genetic basis of heterosisand inbreeding depression were discussed also. The maize quadraplex tetraploids and duplex tetraploids were developed using Kato’s protocols. The phenotype ofheterosis and inbreeding depression over generations in their parents and progenies of F1, F2 and F3 were investigated.The results indicates that different duplex tetraploids have different genetic backgrounds, but they acquire acquire maximumheterosis at same traits, such as the the leaf length, leaf width, culm circumference and days to flowering. PN rises muchfaster from the F2 to F3 segment than the AW does for the plant height in duplex tetraploids. In comparing duplex andquadraplex over a generation the quadriplex is showing the greatest heterosis in plant height, leaf height, leaf width and days to flowering. Most of the examples achieve the maximum heterosis at Qu F2, with the exception of culm circumference, which achieves greatest heterosis at PNAW F1. Meanwhile, this experiment shows that quadraplex tetraploids has distinctadditional favorable alleles that are not contained in duplex tetraploid, this is demonstrated by the heterosis found incrosses between the two duplex tetraploid. This finding helps demonstrates that quadruploids superiority and unique breeding behavior, in which, the progressive heterosis and inbreeding depression in maize are due mainly to linkage disequilibrium. severe inbreeding depression in duplex tetraploids is due mainly to the rapid loss of complementary chromosomes or gene interactions in the first few generations of inbreeding. Correspondingly, the progressive heterosis in quadraplextetraploids is due mainly to a progressive increase in complementarities of homologous chromosomes or genes interactions. Greater complementarities of homologous chromosomes or genes interactions in tetraploids maize alse helps explainrecent molecular biology research indicating that some of traits in quadraplex tetraploids are more responsive to genetic universities than in duplex tetraploids. In addition, the dosage effect of polyploid in relation to the gen etic basis of heterosis and inbreeding depression were discussed also.