The detection and quantitation of drugs of abuse in urine is of growing interest in forensic and clinical toxicology.With the development of highly sensitive chromatographic methods, such as gas chromatographyÂmass spectrometry (GCÂMS), more and more substances can be determined in urine. This reviewincludesmethod for the determination of themorphine in biological samples, where morphine obtained by acidic hydrolysis from urine samples was extracted using mixture of solvents followed by trimethylsilylation. The derivatized extract was submitted to GC/MS analysis of EI-SIM mode. Different factors were studied to five the optimum condition for determination as pH, temperature, solvent of extraction and time hydrolysis.The calibration curves ofmorphine derivatized (MOR-TMS) in urine sampleswere linear in the concentration range from5 to 100 ng/ml. The limit of quantitation was 5 ng/ml.With measuring the optimum makes this method is high sensitive to morphine and become good confirmatory method for determination ofmorphine in urine.