The extreme vertices mixture design was applied for optimization of the NBR blend for hardness response. The 15 treatment combinations out of 29 candidate points investigated (as proposed by Minitab 14 software) Contained varying proportions of carbon black, sulfur, MBTS (Dibenzothiazyl disulfide), and Antioxidant as four variable factors while other factors were kept constant. The significant model coefficients are interpreted in term of interacting linear and quadratic effects of the NBR variable blend constituents. Based on the three dimensional surface, contour, and response trace plot, MBTS exhibits an adverse negative effect, while sulfur exhibits a strong positive effect on the hardness.Carbon black and antioxidant have, respectively, weak and moderate negative effect on the response. The model was used to predict the treatment combination of the NBR blend in the optimum hardness response. (Hardness response was 54.07, A: 3.52, B: 1.5467, C: 91.9733, D: 2.96). There is no significant difference between the result of the model and which obtained in the laboratory.