The present work summarizes an experimental study on the dynamic mechanical behaviour of sisal – glass fiber reinforced PP composites (SGRP). Variation in mechanical strength, storage modulus (E’), loss modulus (E’’) and damping parameters (tan δ) with the addition of fibers and MAPP were investigated. Mechanical tests revealed an increase in the tensile, flexural and impact strength in the SFRP composites with an increase in the fiber loading from 10% to 30%. Further the SGRP composites prepared using 15 wt% of glass and 15 wt % of sisal fiber, exhibited improved mechanical performance as compared with the virgin matrix as well as 30% SFRP composites. The fiber matrix morphology of the interface region in the composites was examined employing SEM analysis of the tensile fracture specimens. Thermal stability in the composites was studied using TGA/DTG thermo grams. Dynamic mechanical analysis data showed an increase in the storage modulus of the treated composite. The tanδ spectra presented a strong influence of fiber content and coupling agent on the α and γ relaxation process of PP. FTIR spectra of the treated and untreated sisal fibers was also studied to ascertain the existence of the type of interfacial bonds.