Objectives. Fluconazole is an antifungal agent which has become the mainstay treatment of opportunistic fungal infections in immuno-compromized patients. Fluoxetine is a selective serotonine reuptake inhibitor used in the treatment of psychiatric disorders. In the current study we investigated the effect of chronic administration of fluoxetine on the steady state pharmacokinetics parameters of fluconazole. Methods. The pharmacokinetics of Fluconazole, following 10 mg/kg single and multiple oral dosing for 10 days, was determined in dogs. Subsequently, the effect of 2 mg/kg fluoxetine given for 10 days, on the pharmacokinetics of Fluconazole was investigated. Results. The co-administration resulted in significant reduction of 40.1% and 35.6% in AUC 0-, and Cmax, respectively compared to fluconazole alone. A significant alteration of Vss/F was also seen as it increased from 0.242 ± 0.04 to 0.654 ± 0.17 l/kg (P<.01). Accordingly, a significant reduction in Kel from 0.048 ± 0.01 hr-1 to 0.031 ± 0.01 was detected (P<.01). Conclusion. fluoxetine reduced plasma concentration of fluconazole. The mechanism of the interaction is probably the inhibition of OATP or other transporters in the intestinal wall. This interaction may have significant clinical importance because reduction in fluconazole may lead to treatment failure of fungal infection.