Here, we report the effect of protein concentration on oil droplet size and adsorbed protein density in oil-in-water emulsions stabilized by bovine serum albumin (BSA) under various pH conditions. The droplet size changed with BSA concentration in a different way depending on pH although it eventually converged on the same value (ca. 15 mu m) irrespective of pH. It was suggested that the adsorbed BSA monolayer at low and high pH could not effectively protect oil droplets against coalescence during homogenization.