Background: Ketamine is an analgesic and anaesthetic drug. It has become more and more popular for drug abuse in recent years. Teenagers have abused it as a recreational and "club drug" because of its hallucinogenic and stimulant effects. It is also misused as a "date-rape" drug to facilitate sexual assaults. Objective: The present study aimed at determination of ketamine in urine by visible UV- spectrophotometer based on ion-pair complex and how long it could be detected after a single oral dose. METHODS: 10 volunteers had received ketamine hydrochloride (100 mg) orally after an informed consent; individual urine samples were collected at different periods (2 h, 6 h, 12 h, 18 h, 24 h, 36 h, 48h, 3 days, 4 days, 7 days, and 10 days). The urine samples were hydrolyzed with concentrated HCl, extracted with chloroform at pH 9.2. The organic phase was treated with bromocresol green in the presence of acetate buffer (pH 2.8). The coloured product is measured at 417 nm. RESULTS AND CONCLUSIONS: Using the visible UV spectrohotometeric method based on the formation of coloured ion-pair complexes with bromocresol green, ketamine was detected up to seven days after drug administration, ranging in mean concentrations of 0.26 - 6.6 µg/mL. It is concluded that, this method can be used for identification and determination of ketamine in the biological samples in cases of drug facilitated crimes.