Abstract:The contents of free salicylic acid (SA) and conjugated SA were determined by using TLC and HPLC at different time after inoculation with Pseudomonas syringae pv.lachymans in the first true leaf of cucumber ( Cucumis sativa L. ) plant. A 30% – 197% increase in free SA content in the inoculated leaves was observed. The change of conjugated SA was similar to that of free SA. There occurred a decrease not only in free SA but also in conjugated SA three days after inoculation. The systemic appearance of free SA in the uninoculated leaves was also found two days after inoculation. The content of free SA in the uninoculated leaves increased by 29% to 46% at the initial stage of inoculation; it reached its peak in three days but it stopped increasing five days after inoculation. The content of the conjugated salicylate in the uninoculated leaves significantly increased by 62% to 107% ,while the increase in conjugated salicylate began five days after inoculation. The authors‘ findings suggested that inoculation with P. syr/ngae pv. lachymans in the first true leaf of cucumber plant could improve the systemic acquired resistance by enhancing SA level in the uninoculated leaves.