Distinguishing between FLT(fluorothymidine) and FLT-MP(flruorothymidine - monophosphate) by imaging methods is important for evaluating the tumor cell proliferation rate. The aim of this study is to develop and validate a suitable 19F MR Spectroscopy for measuring TK1 activity via quantitation of FLT and FLT-MP in vivo. We observed the good correlations between SNR and FLT concentration (r2= 0.94). In phantom study, the locations of FLT and FLT-MP was -175.99, -175.24 ppm, respectively. In vivo study, FLT spectrum in mouse tumor was observed in 25 min after injection, whereas FLT-MP spectrum occurred in 90 min after injection. This result shows that 19F MR Spectroscopy is suitable for monitoring of FLT-MP generation in in vivo.