The benefits of exercise in the prevention of cardiovascular diseases (CVDs) have been investigated for many years. With a growing evidence that coagulation-fibrinolysis imbalance could be contributory in the development of CVDs, the effects of exercise on fibrinolysis are to be perused. The aim of the present work is to study the effect of swimming on the fibrinolytic activity parameters in obese and non-obese rats. Sixty male Sprague-Dawley rats were divided into two groups (n= 30 for each). One group was fed on normal chow diet (Non-obese, wt = 180±5 g), and the other was fed on high-fat (53%) diet for induction of obesity (Obese, wt = 280±18 g). Each of the two groups was further subdivided into 3 subgroups (n = 10, each): Control group, Acute Exercise group (obliged to swim across a glass tank filled with tap water maintained at 35°C, until the signs of exhaustion appear on the animal), and Chronic Training group (obliged to perform the swimming exercise sessions, three times weekly for 12 weeks). In all groups, after completing the particular regime, retro-orbital blood samples were withdrawn, under ether (10%) anaesthesia, and the rats were then humanely killed, under terminal anaesthesia by cervical dislocation. Plasma was separated for the determination of various fibrinolysis parameters: tissue Plasminogen activator (t-PA) antigen, Plasminogen activator inhibitor-1 (PAI-1) antigen, D-dimmer of fibrin/fibrinogen degradation products (FDPs), and euglobulin clot lysis time (ECLT). Data are expressed as mean±S.D. and Significance (P<0.05) tested with ANOVA. Reduced fibrinolytic activity was detected in obese control rats, compared to their non-obese counterparts. This was elicited by increased PAI-1 level from 1.66±0.17 to 2.85±0.09 ng.ml-1, decreased t-PA level from 1.06±0.11 to 0.85±0.08 ng.ml-1, decreased FDPs from 1.85±0.05 to 1.53±0.09 ng.ml-1, and prolongation of the ECLT from 62.6±2.67 to 73.8 ±2.61 min. Acute exercise caused similar significant activation of the fibrinolytic activity in both non-obese rats, and obese rats (decreased PAI-1 by 15% and by 13%, increased t-PA by 47% and by 53%, increased FDPs by 11% and by 6%, and shortened ECLT by 4% and by 8 %; respectively). In non-obese rats, chronic training, as compared to acute exercise, further improved the levels of t-PA (increased by 39%) and ECLT (shortened by 20%), without significant changes in PAI-1 and FDPs. However in obese rats, chronic training, as compared to acute exercise, was associated with better effects on fibrinolytic activity, featured by decreased PAI-1 by 36%, increased FDPs by 12%, and shortening in the ECLT by 19%. It could, therefore, be concluded that obesity produces significant inhibition in the fibrinolytic activity, which is corrected reasonably by acute exercise, and tremendously by frequent physical training. An advantageous consequence, that is valid also in absence of obesity.