The increasingly extensive use of synthetic organic fibres as reinforcement in cement composites requires a more detailed characterization of the fibres in order to estimate any interaction resulting from their addition to cementitious matrices. Research has thus been carried out on acrylic fibres derived from a homopolymer (PAN), and copolymers (AN-MA, AN-MA-IA), and on fibres derived from acrylic fibres (Oxid. PAN), by means of DSC and FT-IR, and SEM. Differential scanning calorimetry studies have been carried out, in both air and N-2 flow at different heating rates, by considering the typical exothermic effect and by estimating comparatively both the characteristic temperatures and the relative heats of reaction. These data, integrated and compared with FT-IR and SEM studies, call give useful information about the chemical and physical characteristics of the fibres.