PURPOSE. The aim of this in-vitro investigation was to describe the effect of reinforcement with different fibers on impact strength of heat polymerized poly-methyl methacrylate (PMMA) denture base resin and to analyze the effect of surface treatment of the fibers on the impact strength. MATERIALS AND METHODS. The specimens were fabricated from the dies formed as per standard ASTM D4812. 2% by weight of glass, polyethylene and polypropylene fibers were incorporated in the PMMA resin. The Izod impact testing was performed on the unnotched specimens and the values obtained were analyzed using appropriate one way ANOVA, followed by unpaired t-test. Fractured ends of the samples were subjected to the SEM analysis. RESULTS. The polypropylene fibers with plasma treatment showed the highest impact strength ($9.229{ imes}10^2$ J/m) followed by the plasma treated polyethylene fibers ($9.096{ imes}10^2$ J/m), untreated polypropylene fibers ($8.697{ imes}10^2$ J/m), untreated polyethylene fibers ($7.580{ imes}10^2$ J/m), silane treated glass fibers ($6.448{ imes}10^2$ J/m) and untreated glass fibers ($5.764{ imes}10^2$ J/m). Also the surface treatment of all the fibers has shown the significant improvement in impact strength. Findings of the SEM analysis justified the improvement in impact strength after surface treatment. CONCLUSION. Reinforcement with the fiber is an effective method to increase the impact strength of PMMA denture base resin. The surface treatment of fibers further increases the impact strength significantly.