The protective effects of tripterygium glycoside-loaded solid lipid nanoparticles (TG-SLNs) on male reproductive toxicity were investigated in rats. Thirty-six male Sprague-Dawley rats were randomly divided into three groups of 12: control group, tripterygium glycoside (TG) group, and TG-SLN group. After the animals had been orally administered with the substances for 28 consecutive days, their sperm count and sperm motility, organ coefficients, serum testosterone levels, testicular ultrastructure, and reproductive ability were observed. The results showed that the sperm motility rate in the TG group was only 3%, whereas the rates in the TG-SLN and control groups were 33 % and 71%, respectively. Compared with those in the control group, the motion counts of path velocity, track speed, progressive velocity, straightness, linearity, beat cross frequency, amplitude of lateral head displacement, and sperm concentrations in the TG-SLN group were not significantly different while those in the TG group significantly decreased (p < 0.01). TG-SLNs did not cause testicular atrophy and instead maintained normal serum testosterone levels. The effect of TG-SLNs on the testicular ultrastructure was very evident; the morphologies of Sertoli, spermatogonial, mitochondrial, and sperm cells were normal. In terms of reproductive ability, one rat (17%) from the TG-SLN group and five rats (83%) from the control group became pregnant, whereas none of the rats from the TG group became pregnant. These data indicate that TG-SLNs have potentially protective effects on male reproductive toxicity in rats.