Abstract: To elucidate the uptake and translocation ability of 3-5-(4-chloro phenyl)-2,3-dimethyl-3- isoxzaolidinyl pyridine-3(SYP-Z048) in tomato seedlings and absorption mechanism of SYP-Z048 by roots, the contents of SYP-Z048 accumulated in roots, stems and leaves were determined respectively, using high performance liquid chromatography (HPLC) after application of SYP-Z048 to roots and leaves of tomato seedlings; the contents of SYP-Z048 were also determined in roots after incubation in SYP-Z048 solution amended with carbonyl cyanide m-chlorophehylhydrazone (CCCP), tryptophan and glucose, and under different temperature or pH values. The results showed that SYP-Z048 could be detected in the leaves and stems after SYP-Z048 application at 50, 100 and 200 mg/L to roots for 2 h, the contents were 78.8, 208.0, 283.7 μg/(g FW)and <0.2, 6.9, 10.3 μg/(g FW) (the amount of SYP-Z048 per gram of plant tissue), respectively; SYP-Z048 could be detected in leaves of the plant after application for 16 h at ≥100 mg/L. Moreover, after application onto the middle leaves of the plant for 72-124 h, SYP-Z048 could be detected in many parts except stems of the plant when treated at ≥500 mg/L, which indicated SYP-Z048 had been transported in the plant. The absorption of SYP-Z048 by roots was neither affected by CCCP, tryptophan or glucose, nor by low temperature or different pH values, compared to that of the control. The results of present study suggested that SYP-Z048 has strong acropetal translocation and weak basipetal translocation ability in tomato seedling, and the absorption is dominantly passive.