Abstract: One resistant cultivar‘( 25-1’) to tomato late blight and a susceptible cultivar‘( Jingle No.502’) were applied to study the relationship between the level of polyphenols, flavonoids and sterol and the resistance of tomato plants to late blight. Results indicated that: (1) no significant difference of the levels of polyphenols and sterol was observed in the uninfected leaves of the two cultivars involved, but the level of flavonoid in the resistant cultivar‘25-1’was significantly higher that of the susceptible cultivar‘Jingle No.502’; (2) after pathogen inoculation, the level of polyphenols and flavonoids in both cultivars showed a similar rising-down trend, the peak appeared later in‘Jingle No.502’than that in‘25-1’, the level of total sterols presented a downward trend in both cultivars, and the level of total sterols in the susceptible cultivar‘Jingle No.502’ decreased more rapidly with the development of the disease.