We conducted a randomized controlled trial to compare local recurrence rate after transurethral resection of superficial bladder cancer treated by either intravesical instillation of an anticancer drug alone (method A) and the intravesical instillation plus oral chemotherapy (doxifluridine, 5'-DFUR, an intermediate metabolite of capecitabine) (method B). Results between groups showed no difference in recurrence-free survival curves in 196 patients subjected to primary analysis. However, patients subjected to secondary analysis (method B, over 3 months administration of 5'-DFUR) showed a significantly better prognosis than method A (p=0.0244, Wilcoxon). Regarding correlation between thymidine phosphorylase (TP, an enzyme to convert 5'-DFUR to 5-fluorouracil) level and prognosis, method A patients showed poorer prognosis in higher TP level cases than in lower TP levels. However, there was no significant difference in prognosis between those with higher and lower TP levels. In method B patients, there was no difference in prognosis between those with higher and lower TP levels. Method A patients tended to show a slightly better prognosis than those with lower TP levels, while method B patients tended to have a slightly better prognosis with higher TP levels, but no significant difference was observed. These findings suggested 5'-DFUR showed a mild efficacy in patients with higher TP levels and that patients with higher TP levels resulted in poorer prognosis.