In our recent study, a new sustained release dosage form of nitrofurantoin (nft) as matrix tablets by 2(2) factorial design has been prepared by using different drug:polymer ratios. The effect of the polyvinylpyrolidone contents of nft matrix tablets on dissolution rate and bioavailability of the drug have been evaluated. The ideal formulation which fitted at USP XXII dissolution norms was tested by in vivo experiments. The satisfactory correlation was also obtained between the in vivo and the in vitro results. This study suggested that the amounts of nft excreted in urine can be calculated by using in vitro dissolution results and sampling time.