Spectroscopic measurements of pharmaceutical compound 5-fluorouracil (5-FU) drug was achieved in the some solvents in different polarit. The drug gave clear absorption peak at 259, 269, 270 and 266 nm in hexane, dimethyl sulfoxide (DMSO), N, N-Dimethylformamide (DMF) and ethanol, as well as phosphate buffer at the same value respectively, which was consistent with the standard values. The results of extension coefficient (ε) and wave length (λmax) showed reduction in polar medium as compared to non-polar medium. The calibration curve of 5-FU drug was achieved by using serials solutions dissolved in phosphate buffer (pH = 7.4 and T = 37 oC) within the range 1×10 – 6 - 1×10 – 4 M. The stability of 5-FU drug was studied in phosphate buffer at pH = 5, 6, 7, 7.4 and 8 with 1×10 – 5 M and T = 37 oC, according to the equation of first order reaction. The hydrolysis of 5-FU disappeared at alkaline solution, but had noticeable hydrolysis in acidic solutions with the rate constant 25, 14 and 20 at pH of 5, 6 and 7, respectively. The calculation of molar extension coefficient and half time (t 0.5) showed same sequence of 5-FU hydrolysis. Then, rearrangement of obtained results offered complicated reversible equilibrium state by the combination between thermodynamic and kinetic behaviors of 5-FU hydrolysis; with Keq = 8.46, 6.11and14.28 at pH of 5, 6 and 7 respectively. The acidic hydrolysis of 5-FU occurred spontaneously within free energy (ΔG) and did not exceed 10 KJ/mole, which means the electro motive forces of interactions were weak, not able to release energy such as Van der Waals forces or hydrogen bonding.