Aim To explore the effect of oxidized low density lipoprotein(ox LDL) on cholesterol accumulation in mouse peritoneal macrophages and its relationship with activity of lysosomal cathepsin. Methods Low density lipoprotein (LDL), acetylated LDL (ac LDL) and oxidized LDL (ox LDL) were prepared and treated the macrophages in the same way. Lysosome and cytoplasm were acquired from the treated macrophages and the contents of total protein,cholesterol and the activities of lysosomal cathepsin L and D were determined. Results Compared to control, both treatment of ac LDL and ox LDL significantly increased the cholesterol level in macrophages (22.2±0.4 μg and 22.55±0.15 μg to control 7.0±0.4 μg, p<0.01), however, ox LDL and ac LDL resulted in cholesterol accumulation in different manner. The ac LDL caused cholesterol ester (CE) accumulation predominating in cytoplasm (18.9±0.4 μg and 3.33±0.20 μg respective in cytoplasm and lysosome, 0.73±0.05 μg and 18.1±0.4 μg respective in FC and CE form), while ox LDL leaded free cholesterol (FC ) accumulation preferring in lysosome of macrophages (3.65±0.14 μg and 18.90±0.15 μg respective in cytoplasm and lysosome, 14.13±0.14 μg and 4.77±0.33 μg respective in FC and CE form) and simultaneously we found that ox LDL markedly inhibited the activities of cathepsin L and D (in the unit of a.u/mg pro, 11.1±2.3 and 2.1±0.5 to control 102.3±8.2 and 27.33 ±1.6,p<0.01); and gave rise to the content of total protein in lysosome. Conclusion Oxidized LDL cause the cholesterol accumulation in lysosome mainlly in free manner and this effect may be related to its effect of inhibiting the activities of cathepsin L and D.