The objective of this study was to design acetaminophen extended release bi layer tablets containing immediate release layer and extended release layer. Tablets were prepared by wet granulation technique using different grades of hydroxypropylmethyl cellulose (HPMC 15 cps, HPMC 100 cps and Methocel K4m CR) as release rate retardant and tablets were evaluated for hardness, friability, weight variation, thickness and drug content uniformity. In vitro release studies were performed using USP type II apparatus (paddle method) in 900 mL of 0.1N HCl at 50 rpm for 4 hours and compared with USP specification. In vitro release studies revealed that the release rate decreased with increase of polymer loading and viscosity. Formulation ER-4 (containing 10% HPMC 100 cps and 1.5% sodium starch glycolate) and ER-6 (containing 1.5% Methocel K4M CR and 0.5% sodium starch glycolate) were found to follow compendial specification for drug release profile. Drug release was analyzed using zero-order, first order, Higuchi and Korsmeyer-Peppas equations to explore and explain the mechanism of drug release from the bi layer matrix tablets. Mathematical analysis of the release kinetics indicated that release from the matrix tablets followed Fickian diffusion. So the bi-layer tablets could be a potential dosage form for delivering acetaminophen.