Detailed contact angle measurements are performed for protein drops on PC, PMMA, Silicon Nitride and Glass substrates by goniometer-sessile drop technique. Drop sizes are ranged from 0.1 to 6 µl with radius of curvature less than 1 mm. The BSA protein concentrations are 0.0, 0.1, 1.0 and 10 mg/ml. The results show that weak dependence of the drop size for deionized water drop on all substrates and increased dependence of the drop size for protein drop with different protein concentration. The significance of drop size effect is varied from substrate to substrate; the effect is the strongest for PC substrate which is a nearly hydrophobic surface. The drop size dependence can be partly explained by modified Young's equation.