Objectives : Laser therapy started in 1958 when Schawlow and Townes suggested medical value of Laser therapy. He-Ne laser has been utilized as a clinical treatment for various diseases by Plog since 1975. Low Level Laser Therapy (LLLT) has been used as medication for controlling obesity in the Korean Medicine. So this study is planned to investigate the effects of LLLT on the level of serum lipid and weight gain Methods : Experimental groups were divided into normal group(Normal), high fat diet group(Control), high fat diet and LLLT by helium-neon (He-Ne) on the tail is carried out once a 2 day during 5 weeks. The animals were divided into six groups: no ischemia-induced and no LLLT-treated group (Normal), the ischemia-induced and no LLLT-treated group (Control), the ischemia-induced and 5 mW 5 min LLLT-treated group (LLLT5-5), the ischemia-induced and 30 mW 5 min LLLT-treated group (LLLT30-5), the ischemia-induced and 5 mW 10 min LLLT-treated group (LLLT5-10), 30 mW 10 min LLLT-treated group (LLLT30-10). The effect of LLLT is observed by weight gain, food intake, food efficiency, serum of lipid concentrations, liver function and HDL to total cholesterol ratio of rats fed high fat diet for 5weeks. Results : Body weight and food intake were decreased in LLL5-5, LLLT30-5, LLLT30-10. Food efficiency was decreased in LLLT30-10. The level of serum Triglyceride, Free fatty acid, AST, ALT, ALP were decreased in LLLT30-10. Serum HDL-cholesterol was increase in LLLT5-10, LLLT30-10. Also serum ALT was decrease in LLLT5-5 Conclusions : LLLT(30 mW-10 min) is effective on Body weight, food efficiency ratio, the level of serum lipid and protection of liver function by obesity induced by high fat diet, and LLLT(5 mW-5 min) act on decrease of Body weight, food intake and ALT