Copolymers of sunflower oil with methyl methacrylate and decyl acrylate were synthesized and characterized. Intrinsic viscosity and viscometric molecular weight were determined by using Huggins and Mark- Houwink equation respectively. Viscosity index (VI) of the additive doped base oils were evaluated and compared with that of the mineral base oils. VI values of the additive doped base oils depend on the nature of mineral base oils used and the type and concentration of VI improvers. For a comparison, respective homopolymers e.g. polymer of sunflower oil, poly(methyl methacrylate) and poly(decyl acrylate) were also prepared, characterized and evaluated in the similar fashion.