An instrumented injection mould was designed to determine the crystallization kinetics of semi-crystalline polymers and short fibre reinforced bulk composites. This set-up is an interesting alternative to other characterization devices since it is more representative of injection process conditions, and bulk samples are more suitable for studying reinforced polymers. We developed a methodology to estimate the Nakamura kinetic function K(T) by solving an inverse 1D heat conduction problem coupled to the kinetic equation. Estimated parameters are obtained in a temperature range which depends on the cooling rate. We first validated the experimental approach with a well characterized isotactic polypropylene. Then, we used this setup to determine the kinetic function of a technical polymer (poly m-xylylene adipamide–MXD6), for which the crystallization is complex since it contains nucleating agents. Our results are compared with a literature empirical model and with those obtained by DSC.