NEW composition polymers formulated from the reaction of different …… mixed polymers by using gamma (ᵞ) radiation technology. A fixed ratio of polyvinylalchol (PVA), chitosan was mixed with different ratios of N-vinyl-2-pyrolidene (NVP) with and without diethyleglycal dimethylacrylate (DEDMA). The chemical structures of the prepared composition polymers were conformed using FT-IR and the molecular weight determination by (GPC). The results of the spectroscopic analysis indicate that they were prepared through right method and they have high purity. The new prepared composition polymers were evaluated as a viscosifier and filter loss additives for water-based drilling fluid formulated from local Egyptian clay to improve their rheological properties. The evaluation includes the study of rheological, filtration of the water – based mud treated with the new prepared composition polymers and the results were compared to the reference commercial water based- mud. The results of treatment of water-based mud with the prepared new composition polymers showed a good efficiency.