In the present study, Central Composite Design (CCD) of Response Surface Methodology (RSM) was employed to investigate the effects of different operating conditions on the removal of nitrate (NO3-) ions from aqueous solution onto Pleurotuseryngii dried fungal biosorbent. A three level, three factors CCD was used to evaluate the effects and interactions of the process variables, i.e., solution pH, biosorbent dose and initial NO3- concentration. The second order mathematical model was developed by regression analysis of the experimental data of 17 batch runs. Analysis of Variance (ANOVA), F-test, Student’s t-test and lack of fit test showed that NO3- ions biosorption is only slightly concentration dependent, but markedly increases with solution pH and biosorbent dose. The optimum pH (7.47), biosorbent dose (0.29 g) and initial concentration (772.02 mg L-1) were found by desirability function. Under these optimum combinations of process parameter conditions, maximum removal of 88.38 % was obtained that assisting its use in larger scale. P. eryngii has been characterized by using different physicochemical methods. The characterization suggested a possible contribution of carboxyl and hydroxyl groups in the process of biosorption. Hence, it is suggested that P. eryngii has potential for biosorption as a low-cost and effective sorbent for NO3- removal from aqueous solution.