This paper presents the experimental study of mechanical and thermal properties of organically modified montmorillonite clay (Nanoclay) (0, 1, 2, 3, 4 and 5 wt.%) in the vinyl ester matrix by ultrasonic stirrer. The changes in mechanical properties are investigated by using tensile and impact testing machine. It was found that the addition of nanoclay particles significantly improved tensile properties of pure vinyl ester, but impact properties of pure vinyl ester were affected negatively with the nanoclay content in the nanocomposite. It was found that the absorbed energy and impact resistance of the nanocomposites decreased with increasing the nanoclay content. DSC curves showed the glass transition temperature change in the nanoclay reinforced vinyl ester nanocomposites as compared to the pure vinyl ester. XRD analysis was performed to identify the structure of nanocomposites. SEM results showed the change in fracture surface morphology of nanoclay reinforced vinyl ester nanocomposite. Also, homogeneous distribution of nanoclays in the matrix was showed by SEM micrographs. This observation helped in identifying the morphology of the nanocaly in the vinyl ester matrix.