The influence of thermal history on the interfacial load transfer efficiency and fibre failure in carbon/polypropylene microcomposites has been studied using Micro Raman spectroscopy. Microcomposites were manufactured by cooling from the melt at different constant cooling rates or isothermally crystallized. Thermal residual strains were measured during and after manufacture of the microcomposites. The residual strains resulted in compressive fibre failure. Based on the experimental data, interfacial load transfer efficiency was determined quantitatively for the different cooling procedures. Results indicate that thermal history has a Very large influence on the interfacial load transfer efficiency of the microcomposites. This was shown to be due to the influence of thermal history on transcrystallinity and interfacial residual stresses. A transcrystalline interphase provides a more effective load transfer compared to the non-transcrystalline interphase. Furthermore, decreasing cooling rates leads to an increase in load transfer efficiency due to increased transcrystallinity and higher crystallization temperature resulting in higher interfacial stresses.