The aim of the research was to to assess the effect of ethanol extract Premna pubescens leaves on humoral immunity and the body weight of rats (Rattus norvegicus L.). The white rats use 24 tails and devided into 4 groups with each group replicates 6 times. There are A0 as control which give with aquadest, A1 give with ethanol extract of Premna pubescens leaves, A2 give with ethanol extract of Premna pubescens leaves and Sheep Red Blood Cells (SRBC), and A3 give with SRBC only. White Wistar rats aged 3 months with body weight 100-300 grams. Aquadest and ethanol extracts of Premna pubescens given orally every day and SRBC given by injections on the 8th and 15th day . The rats blood taken by decapitation on 31th day. Measurements antibody titer of the rat as humoral immunity used hemagglutination method using a V microplate 96. The results were analyzed statistically with ANOVA. The result showed that the antibody titer at A2 increased significantly , where t (65,78) > t table (4,94). This suggests that the ethanol extract of Premna pubescens leaves influence the humoral imunnity of Wistar strains rats using SRBC, The result of body weight statistically, tcount 0.23 < ttable 3.10. It means that ethanol extract of Premna pubescens leaves did not influence the body weigh.