Nano scale dispersion due to the size transformation of the reinforced particles from micron size to nano size in the polymer matrix to enhance the mechanical properties of fiber-reinforced hybrid composite is an interesting research topic of the current time. In this study, the nanocomposites test coupons were prepared through the open molding route. The nano scale dispersion is achieved at an optimum concentration of alumina particles (2 wt%), which results in improved thermal stability, impact strength, flexural modulus and flexural strength of composites. The maximum enhancement in impact energy was observed to be 84 % correspond to the addition of 2 wt%, 20 % for the flexural strength correspond to the addition of 3 wt% and 35 % for the flexural modulus correspond to the addition of 5 wt% alumina particles to the epoxy matrix. For the addition of 5 wt% of short glass/carbon fibers to the epoxy, an improvement of 130 % and 170 % for the flexural strength and 55 % and 95 % for the flexural modulus was observed. Furthermore, addition of optimum concentration (i.e. 2 wt%) of alumina nano particle to the 5 wt% glass/carbon fiber reinforced hybrid composites resulted in the improvement of impact properties, flexural strength and flexural modulus of 175 %, 195 %; 18 %, 26 % and 65 %, 85 % as compared to the neat epoxy, and 7 %, 8 %; 82 %, 105 % and 17 %, 5 % as compared to the short fiber reinforced composites. These enhancements in the mechanical properties are mainly due to the better stress transfer properties from fiber and nanoparticle to the matrix, due to the existence of strong interfacial interactions between both epoxy/alumina nanoparticles, which depict the higher resistance to fiber pull out as compare to fiber reinforced composites without alumina nanoparticles. © 2015, The Korean Fiber Society and Springer Science+Business Media Dordrecht.