Abstract: The level of serum IgG in conventional Zmu-1： DHP guinea pig was detected by single radial immunodiffusion. The level was increased with age from 15-70 days, and tended to be steady or declined slightly thereafter. The level of serum IgG of the strain at the age of 35 days (about 300 g body weight) was 5.37 mg/ml. Generally there was no significant difference in sex. As compared with the purchased strain, the level of serum IgG of Zmu-l. DHP guinea pig had a more steady pattern and a less difference among individuals.