Aim:To evaluate the effects of tamoxifen citrate on gene expression during nuclear chromatin condensation in malerats.Methods:The effects of an oral dose of 0.4 mg/(kg.d)tamoxifen citrate on rates of in vitro chromatindecondensation,acridine orange(AO)dye uptake,concentration of thiol-groups,levels and/or expression of transi-tion proteins 1,2(TP1,TP2),protamine 1(P1),cyclic AMP response element modulator-ι(CREMι),androgen-binding protein(ABP)and cyclic adenosine 3’,5’monophosphate(cAMP)were evaluated after 60 days of exposurein adult male rats.Controls received the vehicle.Results:Tamoxifen citrate enhanced the rates of chromatindecondensation,increased AO dye uptake and reduced free thiols in caput epididymal sperms and reduced the levelsof TP1,TP2,P1,and CREMι in the testis,while cAMP was unaffected.P1 deposition was absent in the sperm.Thetranscripts of TP1,TP2 were increased,of P1 and ABP decreased,while those of CREMι unaffected in the testis.Conclusion:Tamoxifen citrate reduced caput epididymal sperm chromatin compaction by reducing the testicularlevels of proteins TP1,TP2 and P1 and the CREMι involved in chromatin condensation during spermiogenesis.Tamoxifen citrate affects the expression of these genes at both the transcriptional and post-transcriptional levels. Aim: To evaluate the effects of tamoxifen citrate on gene expression during nuclear chromatin condensation in male strains. Methods: The effects of an oral dose of 0.4 mg / (kg.d) tamoxifen citrate on rates in vitro chromatin decondensation, acridine orange (AO) dye uptake, concentration of thiol-groups, levels and / or expression of transi-tion proteins 1, 2 (TP1, TP2), protamine 1 (P1), cyclic AMP response element modulator- (CREMι), androgen- ABP) and cyclic adenosine 3 ’, 5’monophosphate (cAMP) were evaluated after 60 days of exposure to adult male rats. Control received the vehicle. Results: Tamoxifen citrate enhanced the rates of chromatin decondensation, increased AO dye uptake and reduced free thiols in caput epididymal sperms and reduced the levels of TP1, TP2, P1, and CREMι in the testis, while cAMP was unaffected. P1 deposition was absent in the sperm. these transcripts of TP1, TP2 were increased, of P1 and ABP decreased, while those of CREMι unaffected in the testis.Conclusion: Tamoxifen citrate redu ced caput epididymal sperm chromatin compaction by reducing the testicular levels of proteins TP1, TP2 and P1 and the CREMι involved in chromatin condensation during spermiogenesis. Tamoxifen citrate affects the expression of these genes at both the transcriptional and post-transcriptional levels.