A partial block polyimide-polysiloxane copolymer is provided comprising repeat unit structures having structural formulae (1) and (2) wherein X is an aromatic or aliphatic ring-containing tetravalent organic radical, Y.sub.1 is a diamine residue, Y.sub.2 is a diaminosiloxane residue, Y.sub.1 and Y.sub.2 are contained in the copolymer in amounts of 99-20 mol % and 1-80 mol %, respectively, L and m each are an integer of 2-50. The copolymer has good adhesion to substrates, moisture-proof reliability and a low modulus of elasticity. ##STR00001##