The study is to investigate the pharmacokinetics of S-1 capsule (tegafur, gimeracil and potassium oxonate capsule) in patients with advanced gastric cancer after single and multiple oral administration.  Twelve patients with advanced gastric cancer were recruited to the study.  The dose of S-1 for each patient was determined according to his/her body surface area (BSA).  The dose for single administration was 60 mg every subject.  The dose for multiple administration for one subject was as follows: 100 mg·d⁻¹ or 120 mg·d⁻¹, 28-days consecutive oral administration.  The pharmacokinetic parameters of tegafur, 5-fluorouracil, gimeracil, potassium oxonate and uracil after single oral administration were as follows: (2 207 ± 545), (220.0 ± 68.2), (374.9 ± 103.0), (110.5 ± 100.8) and (831.1 ± 199.9) ng·mL⁻¹ for C_max; (11.8 ± 3.8), (4.4 ± 3.3), (7.8 ± 5.1), (3.1 ± 0.9) and (8.8 ± 4.1) h for t_1/2, respectively.  After six days oral administration, the average steady state plasma concentrations (C_av) of tegafur, 5-fluorouracil, gimeracil, potassium oxonate and uracil were (2 425 ± 1 172), (73.88 ± 18.88), (162.6 ± 70.8), (36.89 ± 29.35) and (435.3 ± 141.0) ng·mL⁻¹, respectively, and the degree of fluctuation (DF) were (1.0 ± 0.2), (2.5 ± 0.4), (3.1 ± 0.8), (2.4 ± 0.8) and (1.5 ± 0.3), respectively.  The cumulative urine excretion percentage of tegafur, 5-fluorouracil, gimeracil and potassium oxonate in urine within 48 h were (4.2 ± 2.8) %, (4.7 ± 1.6) %, (18.5 ± 6.0) % and (1.7 ± 1.2) %, repectively, after single oral administration of S-1.  The results exhibited that tegafur had some drug accumulation observed, and gimeracil, potassium oxonate, 5-fluorouracil and uracil had no drug accumulation observed.