Aims: Conditioned medium of mesenchymal stem cells have a positive effect on repairing damaged tissues because of having metabolites, growth factors and cytokines. The aim of current study was to investigate the healing effect of conditioned medium of adipose tissue-derived stem cells on histomorphometric changes of testis in treated mice with busulfan. Materials & Methods: In this experimental study, 18 adult male mice were divided into the three equal groups including control group (Without

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... eatment), azoospermia sham and experimental groups. The sham and experimental groups were induced azoospermia by two injection of 10 mg/kg busulfan intraperitoneally, with 21 days interval. 35 days after the second injection of busulfan, the experimental group treated with conditioned medium of adipose tissue-derived stem cells, and 60 days after conditioned medium injection, the testes of mice were removed and histomorphometric evaluation was done. The results were analyzed by SPSS 18 software using Mann-Whitney, ANOVA and Tukey's post hoc-test. Findings: The lumen diameter and area of the seminiferous tubules in the three groups did not have any significant difference; however, the total diameter, cellular diameter, cellular area, cross-sectional area and spermatogenesis index of the seminiferous tubules were significantly decreased in the experimental group compared to the control group (p˂0.05), while they were significantly increased compared to the azoospermia sham group (p˂0.001). Also, the number of tubules and numerical density of the seminiferous tubules were significantly increased in the azoospermia sham compared to the control and experimental groups (p˂0.001). Conclusion: Secretory factors of conditioned medium from adipose tissue-derived stem cells could be effective in the restoration of spermatogenesis in busulfan-induced infertile mice.