The aim of this study was to evaluate the transcrystalline effect on the interfacial shear strength in a single carbon fibre (CF) reinforced syndiotactic and isotactic polypropylene (sPP, iPP) composites by the fragmentation test. It was established that the sPP matrix exhibited a very good interfacial bonding with high-tenacity (HT) CF. The interfacial adhesion was enhanced further by transcrystalline growth of sPP induced by a high-modulus (HM) CF. However, a poor interfacial adhesion existed between iPP and HMCF even in the presence of transcrystallinity. Matrix yielding and interfacial debonding were the dominant failure mechanisms for the sPP/HMCF and iPP/HMCF microcomposites, respectively. The fraction and the location of the amorphous phase along with a peculiar lamellar orientation in the transcrystalline layer were suggested to be responsible for improved interfacial shear strength.