OBJECTIVE To understand the mechanism of testis regression in aging male. METHODS Human testis tissues were obtained during related operation with informed consent (normal young male 3 cases and aged male 3 cases). Total RNA was isolated by QIAGEN RNAeasy kit. Differentiations of gene expression were studied by Clon-Tech cDNA microarray methods and the differential expression gene in aged male were classified by Venter's classify system and the candidate genes were investigated by RT-PCR analysis. RESULTS In the results of cDNA microarray we found 117(1.46%) gene differentiations in aged male at least more than 1.0 fold. Among them, the 83 genes were down-regulated and the 34 genes up-regulated. The down expressed genes related to metabolism were 16(19.3%), gene or protein expression 18(21.7%), cell signaling or cell communication 16(19.3%), cell division 19(22.9%), cell structure or motility 6(7.2%) and unknown function 4 genes (4.8%). The up expressed genes related to cell division were 11 (32.4%), gene or protein expression 10(29.4%) and metabolism 3 (8.8%). It is interesting to find that respiratory chain related gene cox7a2 was up-regulated and atp50 down-regulated significantly which as further confirmed by RT-PCR analysis with sequence analysis in the products of the RT-PCR by T-A cloning. CONCLUSION The gene expression profile in aged male testis was changed significantly as compared with that in normal young controls; testis regression in aging male may relate multi-gene differentiations, especially the differentiations of respiratory chain related gene cox7a2, atp50, which may be an important candidate gene in the study of the mechanism of testis regression in aging male.