A sensitive fluorometric method was developed for the determination of urea. The method was based on the hydrolyzation of urea catalyzed by urease with pH and the change of fluorescence intensity of sodium fluorescein as a pH sensitive dye in the enzymatic reaction. The increase in fluorescence intensity of sodium fluorescein was measured at λex= 490 nm and λem= 514 nm. Under the optimum conditions the assay responded linearly to urea concentration in the range of 0.25 to 3 mM with a correlation coefficient of 0.996. This study also demonstrated the feasibility of a fluorometric method for urea determination with fiber optic detection. The probe response also displayed good linearity in the range of 0.10 to 1.75 mM urea.