Prothrombin time (PT) and activated partial thromboplastin time (APTT) are important investigations used for evaluation of coagulation system and monitoring of anticoagulant therapy. This study was conducted at Faculty of Medical laboratories Science, Elneelain University, Khartoum, Sudan. It is aimed to study the effect of freezing storage (at -20c) of citrated plasma on PT and APTT. Blood samples were collected from 50 healthy volunteer, and platelet poor plasma was separated. PT and APTT were performed immediately after plasma separation using part of the plasma; the rest of the plasma stored at - 20?C in 3 different plastic containers and PT and APTT were performed after 1, 2, and 3 weeks on these samples. The results revealed that PT and APTT results for the samples stored for 1, 2, and 3 weeks were significantly different (P.value> 0.05) from the result of fresh plasma and from each others. PT and APTT were raised with increased storage duration. In conclusion, freezing storage at -20?C affect PT and APTT, so it is preferably that PT and APTT performed immediately after sample collection.