Objectives: Nowadays, a lot of attention has been paid to the therapeutic properties of herbs, including evaluation of the effects of these plants on fertility in laboratory animals. Apium graveolens L. (celery) has been widely used in traditional medicine for treatment of various disorders including impotency. Therefore, this study was designed to investigate the effects of aqueous extract of A. graveolens on testicular tissue and spermatogenesis in healthy male rats. Materials and Methods: In this research, 24 apparently healthy male rats were divided into three groups, including eight rats in each. The first group as control received only distilled water 1 ml/animal/day. The second and third groups orally received 100 and 200 mg/kg b.w. of the extract, respectively, for 30 days. The day after the last administration of the extract, the rats were sacrificed, the testes were removed entirely, and the morphometric studies were carried out. Epididymal sperm count and histological studies of testicular tissue were conducted. Results: The comparison between the treated and control groups revealed a remarkable increase in the seminiferous tubules diameter, testes volume (p≤0.001), and the number of spermatogonia, primary spermatocytes and spermatozoa. Furthermore, the increase in the number of spermatids and epididymal weight were only significant at high doses of the extract (p≤ 0.05). Conclusions: The results from this study indicated that administration of celery leaf extract may improve spermatogenesis process and also be useful for some sperm fertility parameters