This paper developed optical fiber sensor based on molecular imprinted polymer as artificial recognition element for the determination of 6-mercaptopurine (6-MP) in human serum. This approach displayed high sensitivity by oxidizing 6-MP to a strong fluorescent compound with H(2)O(2) in the alkaline media. It offered a relatively nice selectivity for 6-MP detection by molecular imprinted polymer's recognition. The relative standard deviation (R.S.D.) was 5% for a same sensor (n=5) when 6-MP concentration was 1.0 x 10(-7)gm L(-1) in serum. The developed method was satisfactorily applied to the determination of 6-MP in human serum without any necessity for sample treatment or time-consuming extraction steps prior to the analysis.