Half life of drug is a pharmacokinetic property of the drug. For any given drug and dose, the plasma concentration of the drug will rise and fall according to the rates of three processes: absorption, distribution, and elimination. The half-life of a drug is the time it takes for its concentration in blood or plasma to decrease by half. The time required for any plasma concentration of drug to fall by 50% is known as half- life of that drug (T1/2). In this review we summarized about the half-life of the drug.