The relationship between release properties of the model antigen, bovine serum albumin (BSA), from formulations in vitro and immune response after administration of various oil adjuvanted vaccines containing liquid paraffin was examined in chickens. The vaccine prepared at an hydrophile-lipophile-balance (HLB) number of 4.8 showed slower release of BSA and higher immune response on injected chickens than that with an HLB number of 6.0. Decreases of aqueous volume ratio in the formulation also led to slower release of BSA and higher immune response. The slower release rate of BSA showed higher ELISA antibody titer even at 20 weeks after vaccination. The ELISA antibody titer inversely was related to the constant release rate, k, calculated from the in vitro release test. The correlation coefficient was 0.863. The immune response of oil adjuvanted vaccines containing Haemophilus paragallinarum agreed well with these results with BSA. Our results indicated that a stronger and more prolonged immune response of oil adjuvanted vaccines was achieved by slower release rate of antigen from the formulation. In addition, there was a good correlation between immune response and the value of k.