La2/3Sr1/3MnO3/La1.4Sr1.6Mn2O7 composites with arbitrary weight percentage were prepared using a one-step sofid-state reaction method.The experimental results demonstrated that addition of K2CO3 during preparation favored the formation of the composites even though the K+ ions were volatilized under the high temperatures of sintering.Full quantitative analysis with the Rietveld method showed that the content of La1.4Sr1.6Mn2O7 phase decreased and the fraction of the La2/3Sr1/3MnO3 phase increased as the amount of K2CO3 was increased.