A method for producing a polycarbonate copolymer which has siloxane constituent units represented by any of formulae (1-1) to (1-4) and prescribed polycarbonate constituent units, the method having a polymerization step for polymerizing a silane-based compound selected from among a prescribed diaryloxysilane compound, a prescribed dialkoxysilane compound and a prescribed silicon compound, a carbonate compound and a diol compound such as an aromatic diol compound or an alicyclic diol compound in the presence of a transesterification catalyst. The polymerization step is carried out in a molten state under reduced pressure while removing alcohols derived from the carbonate compound. ##STR00001##