A predictive in vitro-invivo correlation (IVIVC) can empower in vitro dissolution as a surrogate for in vivo bioavailability / bioequivalence. IVIVCs can decrease regulatory burden by decreasing the number of biostudies required in support of a drug product. The present study concerns the establishment of in vitro-in vivo correlation for three different sustained release nimesulide loaded ethylcellulose microparticulate formulations (M1, M2 and M3) and conventional tablet (100 mg Nimaran®-Novartis, Pakistan). In vitro dissolution study was conducted in phosphate buffer pH 6.8 stirred at 50 rpm and 37 ± 0.5ºC. A validated HPLC method was adopted to conduct bioavailability studies in young healthy human volunteers. Ultimately IVIVC of prepared microparticles and conventional tablet was established using Wagner-Nelson method. M1 and M2 formulations and Nimaran® exhibited good linear IVIVC (R2 = 0.9220, 0.9124, 0.8728, respectively) as compared to M3 (R2 = 0.9449). The results substantiate the success of this mathematical simulation study encourage researchers to conduct biowaiver studies for other BCS class II drugs.