INTRODUCTION The oral route is the most common route of drug administration, because of its advantages in terms of convenient administration. Pharmaceutical products designed are mostly immediate release type, designed for immediate release of drug for rapid absorption. Sustained release formulation is design to achieve steady state blood level and non toxic for extended period of time. Rationale for Selection of Drug :-  The basic goal of this therapy is to maintained steady state blood level for Extended period of time better therapeutic efficiency less side effect reduced dosage regimen.  Mefenamic acid is Non Steroidal Anti- Inflamatory Drug use as Analgesic particularly for Menstrual pain that happen on or before of Menstruation and as analgesic for joint pain.  Rabeprazole is Proton Pump Inhibitor which inhibit the H+/K+ -ATPase pump present on gastric parietal cell of stomach the most potent anti secretory compound for Treatment of Acidity.  Sustained release preparations provide an immediate dose required for the normal therapeutic response, followed by the gradual release of drug in amounts sufficient to maintain the therapeutic response for a specific extended period of time.