An experiment was conducted to study the effect of medium constituents for maximization of pterin deaminase production by indigenous fungal isolate Aspergillus terrus JQ 436691 under solid state fermentation process wheat bran as the substrate. In Plackett–Burman design (PBD), the pterin deaminase production was increased from 50.2 to 102.20 IU/ml. From pareto chart, the wheat bran, sucrose, yeast extract and urea were identified as significant constituents which influences highly for pterin deaminase production and these variables were subsequently optimized using a Box- Behnken design. The maximum experimental pterin deaminase production of 138.20 IU/ ml was very close to the predicted value 141.29 IU/ml and protein content of 137.10 μg/ml using substrate 10g wheat bran, 2.00 % (w/v) sucrose, 0.03 % (w/v) yeast extract and 0.15% (w/v) urea by Box- Behnken design (RSM). The significant interaction was existed between the amount of substrate wheat bran x sucrose, wheat bran x urea, wheat bran x yeast extract and sucrose x yeast extract for pterin deaminase production since the contour lines were elliptical in nature.