A problem of the invention is to provide a propylene copolymer which is excellent in adhesion to crystalline propylene-based polymers and which is excellent in solubility and compatibility with polar resins, a process for producing the same, and a composition containing the subject polypropylene copolymer.The invention is concerned with a polypropylene copolymer, which is characterized by having a polymer principal chain (A) derived from a propylene-based polymer having (1) a prescribed requirement as defined by the .sup.13C-NMR spectral measurement and having (2) a melting point [Tm] by a differential scanning calorimeter of not higher than 100.degree. C., or a crystal melting heat of less than 5 J/g; and a side chain containing a polymer chain (B) which is different from the principal chain, with a weight ratio of (A)/(B) being in the range of from 20/1 to 1/20, a composition containing the subject copolymer, and a process for producing the subject copolymer.