Objective To observe the changes of S-opsin expression in guinea pigs with flickering light-induced and form-deprived myopia, and to investigate the causes. Methods Thirty-six two-week-old healthy guinea pigs were randomly assigned to three groups: Flickering light-induced myopia group (FLM group,n=13), form-deprived myopia group (FDM group,n=12) and control group (n=11).For the FLM group, the cages were equipped with astroboscope (0.5 Hz), and LEDs were used as the light source. The right eyes of the guinea pigs in FDM group wore translucent goggles which did not interfere with the normal activity of their eyelids. No special treatment was given to the guinea pigs in the normal groups.All measurements were performed prior to and then after 6 weeks of treatment. The first measurement day was recorded as 0 week. Biological parameters, such as the refraction, axial length (AL) and corneal radius of curvature (CRC), were measured and fundus photography is performed before and after 6 weeks of the treatment. The expression of S-opsin was observed and analyzed by immunofluorescence technique and image analysis system. Results Before the treatment, no significant difference was found in three biometric measurements including refraction, AL and CRC between the groups at 0 week (P > 0.05). After the treatment for 6 weeks, significant differences were found in changes of both the biometric measurements between the FLM and control groups, and between the FDM and control groups (P < 0.05). However, no significant differences were found in the changes of CRC among the FLM, FDM and control groups(P=0.358), indicating that myopia models were established successfully. No significant differences were found in the changes of values of refraction, AL and CRC between the FLM and FDM groups (P > 0.05). Expression of S-opsin differed in the FLM and FDM groups. For the mean gray values of green channel,compared with the control group respectively, significant differences were found in both the FLM and FDM group (P < 0.001). The mean gray value of green channel of the FLM group was higher, however the mean gray value of green channel of the FDM group was lower. Conclusions Both guinea pig models of flickering light-induced and form-deprived myopia can be established successfully. S-opsin is increased in the flickering light-induced myopia model and decreased in the form-deprived myopia model, indicating that the mechanisms of formation of these two experimental myopia models may be different.