Abstract: Objective To analyse the relationship between stability plasma concentration of 5-Fu, docetaxel and adverse effects, short term effect. Methods Forty patients with gastic cancer or esophageal caner received the same regimen (continuous infusion of 5-Fu 2.5g/m2 for 120 h, leucovorin 200 mg d1-5 and paclitaxel 75mg /m2 d1 every three weeks).The stability concentrations of 5-Fu and docetaxel were detected by high-performance liquid chromatography (HPLC).The relationship between stability plasma concentration of 5-Fu,docetaxel and adverse effects, short term effect was analysed with Fisher's exact test. Results The interindividual variation of 5-Fu stability plasma concentration was large.The concentration of 5-Fu varied from 1.2 mg/L to 99.6 mg/L,and docetaxel varied from 0.34 mg/L to 0.98 mg/L,which were demonstrated normalitydistribution.Patients were grouped in to two groups which were 5-Fu concentration ＜30 mg/L and ≥30 mg/L, the degree of diarrhea and mucositis had obvious difference between the two groups, while short term effect had no difference. When the two groups were divided by docetaxel concentration ＜4.9mg/L and ≥4.9 mg/L, patients with high concentration docetaxel had more severe myelosupression and better short term effect. Conclusion The stability concentration of 5-Fu and docetaxel had large interindividual variability after chemotherapy according to body surface area. The stability concentration effected the adverse events and short term effect. Mornitoring plasma concentration of chemotherapeutics may predict the toxicity and effect.