The pharmacokinetics of ibuprofen were studied under microgravity (μG) conditions and compared with those at normal gravity (1G) in humans. Six healthy human volunteers were given 600 mg oral dose ibuprofen during 1-day simulated μG antiorthostatic bed rest position, then at normal position (1G) in a sequential design with 7 days washout time. Saliva and plasma samples were obtained up to 8 hours after dosing. Ibuprofen was not detected in all saliva samples. Pharmacokinetic parameters in plasma were calculated by either noncompartmental analysis or a 1-compartment model using the Kinetica program. Absorption kinetic parameters were then predicted by ADAM and PE modules using the Simcyp program. Results have showed an increased rate of ibuprofen dissolution and absorption and hence faster onset of action under μG conditions. However, rate of drug elimination and bioavailability was not affected by μG, suggesting no need for dose adjustment.