To clarify a cause of increased serum level of acid phosphatase in CCl$_{4}$-treated rats, the acid phosphatase activity of liver was compared with that serum. Concomitantly, the serum and liver acid phosphatase activity of CCl$_{4}$-treated rats were compared with that of CCl$_{4}$-treated rats pretreated with prednisolone or actinomycin D. In CCl$_{4}$-treated rats, the activity of serum acid phosphatase was significiantly increased whereas that of liver acid phosphatase was rather slightly decreased. the pretreatment of prednisolone led to the decreased activity of serum and liver acid phosphatase in CCl$_{4}$-treated rats. But the pretreatment of actinomycin D rather increased the activity of liver and serum enzyme. In conclusion, it is likely the increased activity of serum acid phosphatase is based on the excess leaking of acid phosphatase into blood by the increased membrane permeability of both liver cell and lysosome in it.