Testosterone (T) plays a vital role in the sexual function and many other health-related phenomena. We conducted this study to examine the effects of low level laser therapy (LLLT) on the testis in elevating serum T level in rats. We performed the current experimental study using 30 male Sprague-Dawley rats (Orient Bio, Korea) aged six weeks, weighing 200 g. In rats of two laser groups, a 670-nm diode laser or an 808-nm one were irradiated to the testes at an intensity of 360 J/cm2/day (200 mW ´ 30 min) for five days. This was followed by the measurement of the depth of tissue penetration, that of serum T level and histopathological examination. Our results showed that the rate of tissue penetration was significantly higher in the 808 nm wavelength group as compared with the 670 nm wavelength group (P<0.05); serum T level was not significantly higher in the experimental groups as compared with the control group; but serum T level was significantly elevated in the 670 nm wavelength group on day 4. Thus the LLLT using a 670-nm diode laser was effective in increasing serum T level without causing any visible histopathological side effects. In conclusion, the LLLT might be an alternative treatment modality to the conventional types of testosterone replacement therapy.