A simple, precise, and rapid ultra-performance liquid chromatography (UPLC) method for the determination of fluoxetine level in human plasma using clomipramine as an internal standard (IS) was developed and validated. Plasma samples containing fluoxetine were spiked with the IS and extracted with hexane and iso-amyl alcohol (98:2,v:v) under alkaline condition. Extracted samples were kept at –80ºC for 10 minute then organic layers were transferred to clean tubes and dried under gentle steam of nitrogen at 40 °C. Residues were reconstituted in 200 µl of 0.05% phosphoric acid and 10 µl were injected in to the UPLC system. The compounds of interest were efficiently separated on 2.1 x 100 mm, Acuity UPLC, C18, steel column (at 30°C) and detected with a photodiode array detector set at 230 nm. The mobile phase consisted of water (pH= 2.4, adjusted with phosphoric acid) and acetonitrile (68:32, v:v) and was delivered at a flow rate of 0.3 ml/minute. No interference in blank plasma or by norfluoxetine or commonly used drugs was observed, and the detection limit of fluoxetine was 0.005 µg/ml. The relationship between fluoxetine concentration in plasma and peak height ratio of fluoxetine /IS was linear (R2 ≥ 0.985) in the range of 0.01 –1 µg/ml. Inter-day coefficient of variation and bias ≤ 13.0%, and < 9.4, respectively. Extraction recovery of fluoxetine and IS from plasma samples was ≥ 87%. Using the method, fluoxetine was found to be ≥ 85% and ≥ 89% stable in processed (24 hours at room temperature or 48 hours at -20 °C) and unprocessed (24 hours at room temperature or 23 weeks at -20 °C) samples, respectively.