Surface active gelatin was formed by covalent attachment of hydrophobic groups to gelatin molecules, The modification was carried out at various degrees of attachment and with various chain lengths. These modified gelatins (MGs) were synthesized in dry DMSO by a simple and rapid method. The new method leads to high yields and allows high degrees of modification. The MGs, which have various hydrophobicities, have better surface activity than the native gelatin, as determined by surface tension reduction. The surface tension reduction is correlated to the hydrophobicity of the modified molecule, which was determined by a fluorescent probe. It appears that both the increase in the number of the hydrophobic groups and the increase in the chain lengths lead to decreased surface tension.