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[Objectives]The aim of this experiment was to investigate the protective effect of retinoic acid on testicular injury in heat stressed mice. [Methods]Forty 7-week-old male ICR mice were randomly divided into four groups:control group(CON), heat stressed group(HTRA0), 5 mg·kg-1·d-1retinoic acid-treated group(HTRA5)and 10 mg·kg-1·d-1retinoic acid-treated group(HTRA10). Mice were gavaged with appropriate doses of retinoic acid or corn oil and then subjected to systemic heat stress at 42 ℃ for 2 h. The mice were slaughtered and sampled at the end of the test. [Results]Compared with the CON group, the testicular weight, minimum diameter, cross-sectional area, diameter, and epithelial height of spermatogenic tubules in the HTRA0 group were significantly reduced(P<0.05), the epididymal sperm motility significantly decreased(P<0.05), the malondialdehyde(MDA)content and the expression levels of antioxidant related genes(nrf2, ho-1, nqo1, sod1, gpx1)in testis tissue significantly increased(P<0.05), while total superoxide dismutase(T-SOD)activity significantly decreased(P<0.05), the mRNA expression level of bax significantly increased(P<0.05), the expression levels of blood-testis barrier related genes(occludin, zo-1, n-cadherin and connexin 43)significantly increased(P<0.05), and the expression levels of spermatogenesis related genes(plzf, c-kit)expression significantly increased(P<0.05). Compared with HTRA0, the cross-sectional area, diameter and epithelial height in the HTRA5 group significantly increased(P<0.05), the MDA content significantly decreased(P<0.05)while T-SOD activity significantly increased(P<0.05), and the mRNA expression levels of plzf and c-kit significantly decreased(P<0.05). Compared with HTRA0, the cross-sectional area, diameter and epithelial height of spermatogenic tubules in the HTRA10 group significantly increased(P<0.05), sperm motility significantly increased(P<0.05), MDA content significantly decreased(P<0.05), T-SOD activity significantly increased(P<0.05), and the mRNA expression levels of nqo1, bax, bcl-2, zo-1, n-cadherin, plzf and c-kit were significantly reduced(P<0.05). [Conclusions]Retinoic acid could improve testicular weight, testicular histomorphology, and epididymal sperm motility in heat-stressed mice. This protective effect may be achieved by increasing the antioxidant capacity of mouse testes, reducing germ cell apoptosis, enhancing the blood-testis barrier, and improving the spermatogenic microenvironment. [ABSTRACT FROM AUTHOR]