Lipoprotein lipase (LPL) and hepatic triglyceride lipase (HTGL) enhance the hydrolysis of triglycerides (TG) transported by chylomicron (CM) and very-low-density lipoprotein (VLDL). We report a case of severe hyperchylomicronemia with high levels of remnant lipoprotein and total cholesterol (T-Chol) in a 15-year-old boy. Precise examination of the lipid profile showed decreased activities of both LPL and HTGL, although the protein mass for LPL and HTGL were maintained. In addition, bezafibrate treatment effectively ameliorated hypertriglyceridemia in this case. This is the first case of hyperchylomicronemia with decreased activities and unaffected protein masses for both LPL and HTGL, without overt immuno-dysfunction.