Disclosed is a photosensitive resin composition. The composition comprises [A] an alkali-soluble resin, [B] a photoactive compound and [C] a solvent. The alkali-soluble resin is a copolymer including at least one structural unit with an aziridine group. The composition exhibits good storage stability, high sensitivity, high UV transmittance, high residual film ratio, improved coating uniformity and excellent pattern-forming properties. Further disclosed is an organic insulating film formed using the composition. The organic insulating film has excellent resistance to solvents and chemicals.