Full characterization, that is the true molar mass distribution and block sequence, of a multiblock copolymer based on poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) and poly(bisphenol A carbonate) (PC) segments (PPO-b-PC), synthesized by polycondensation reaction of both diol-terminated PPO and PC samples with the bischloroformate of bisphenol A, is reported. The initial diol terminated PPO sample contains a few tetramethyl bisphenol A units in the backbone. The molar mass distribution of the starting PPO and PC homopolymers and the multiblock structure of the final PPO-b-PC copolymers were studied by light scattering and viscometry on-line with a SEC system, MALDI-TOF mass spectrometry, and NMR. In a previous study, we have demonstrated that homogeneous PPO-b-PC block copolymers having only one single T-g were obtained if low molar mass PPO and PC starting blocks were used. More important findings of this recent study are the following. MALDI-TOF analysis showed that the synthesized PPO-b-PC copolymers were composed of multiblock PPO-b-PC chains and also of some nonreacted PC oligomers terminated with methyl carbonate groups. Exhaustive and selective aminolysis of carbonate groups of the PC blocks has been also performed in order to determine the number of blocks and the average length of PPO blocks in the copolymers.