In the present work, nano-TiO₂ particles in the anatase form were effectively surface modified via reacting with NCO groups of 4,4′-methylenediphenyl disocyanate (MDI). A solution of azobisisobutyronitrile (AIBN) (0.1 g) in inhibitor-free styrene (10 g) was poured into a 150-mL flask containing poly (vinyl alcohol) (PVA) suspending agent (0.1 g) in deionized water (60 mL) under N₂ flow, while stirring. The reaction mixture was then heated to 80 °C, and stirred for another 1 h. Next, it was divided to two portions; one for the synthesis of pure PS, and the other for the synthesis of PS/TiO₂ nanocomposites. Each aqueous portion was individually mixed with dichloromethane in a separating funnel. For PS/TiO₂ nanocomposites, the organic phase was charged with nano-TiO₂ particles (MDI-treated and/or untreated) (0.05 g), and then fully homogenized using ultrasonic homogenizer. Methanol non solvent was eventually used to precipitate the products. All samples involving pure PS, PS/surface modified TiO₂ nanocomposite, and PS/surface unmodified TiO₂ nanocomposite were thoroughly washed, filtered, and dried in vacuum at 50 °C for 12 h. From SEM images a core-shell relation could be clearly detected between the nano-TiO₂ particles and PS matrix. Meanwhile, the surface modified TiO₂ was dispersed into the PS matrix with better homogeneity compared to that of unmodified one. Undoubtedly, beside the surface modification factor, PVA suspending agent as an effective nanosized particle stabilizer played a basic role in this high homogeneity. Also, FT-IR and XRD analyses led to promising results.