This paper presents the experimental results of the influence of co-rotating twin screw extrusion, a high shear process for dispersing MMT in vinylester, on the properties of the nanocomposites. Four main factors namely, MMT (3, 4 and 5 wt %) loading in vinylester, speed (100, 200 and 300 rpm), temperature (5, 15 and 30 o C) and number of passes (5, 10 and 15) were considered for the design of L27 OA lay-out. Four response factors such as glass transition temperature of the MMT/vinylester gelcoat; and UTS, interlaminar shear strength, and flexural strength of the MMT/vinylester/glass nanocomposites were studied. The Tg of MMT/vinylester increased with MMT loading and the maximum increase was 34.8 % in 5 wt % compared to that of vinylester specimens. MMT loading was found highly significant, followed by the number of passes, based on the ANOVA results for Tg. Grey relational grade for the mechanical properties of MMT/vinylester/glass was highest for the factor level combination of 4 wt % MMT, 5o C, 100 rpm and 15 passes, which was also evidenced by the X-Ray Diffraction (XRD) and Transmission Electron Microscopy (TEM) results of MMT exfoliation. Scanning Electron Microscopy (SEM) of tensile fractured specimens showed good interfacial bonding for the same combination. The mechanical properties increased up to 4 wt % MMT loading in MMT/vinylester/glass and decreased for 5 wt % loading. MMT loading followed by temperature were found significant based on the ANOVA for the mechanical properties.