A simplified enzyme based fiber optic uric acid biosensor is reported. It is constructed by coimmobilizing uricase and horseradish peroxidase [HRP] to bovine albumin via glutaraldehyde. A new fluorimetric substrate, thiamine, is used to indicate the sensing process. Under optimized conditions, the linear range of uric acid concentration is 0.5 to 5.0 ug/mL with a correlation coefficient of 0.997, and the detection limit is 0.15 ug/mL with excellent reversibility and stability. The sensor can be used at least two months at room temperature. It is possibly to determine uric acid directly in serum and urine samples with satisfactory results.