A 3-year experiment (2005-07) was conducted on Reunion Island (France) to evaluate the effect of species, climate and fertilization levels on fibre and protein fractions of tropical (C4; Chloris gayana and Pennisetum clandestinum) and temperate (C3; Dactylis glomerata and Lotium multiflorum) grasses. A near infrared reflectance spectroscopy (NIRS) prediction referential was developed to estimate neutral detergent fibre (NDF), acid detergent fibre (ADF), crude protein (CP), NDF insoluble protein (NDF-IP) and ADF insoluble protein (ADF-IP). The NIRS equations were then used to screen many regrowth grass samples collected at heading stage continuously for 3 years to evaluate their changes during the seasons. Results showed that grass species differed significantly in fibre and protein fractions. NDF, ADF and ADF-IP were the lowest in D. glomerata/L. multiflorum and the highest in C. gayana. The wet season was associated with higher NDF, ADF and NDF-IP in D. glomerata/L. multiflorum and lower NDF-IP in P. clandestinum. Fertilization increased the CP in C. gayana and the NDF-IP in P. clandestinum, but decreased the ADF-IP of both C. gayana and D. glomerata/L. multiflorum. Growth rate strongly changed NDF, ADF, NDF-IP and ADF-IP although no change in CP appeared. In general, NDF, ADF and NDF-IP increased with the growth rate. In contrast, the ADF-IP content decreased from slow to fast growth rate in C. gayana and D. glomerata/L. multiflorum. Growth rate changes were thus considered as a general indicator for fibre and protein fraction variations of these grasses.