Furunculosis caused by Aeromonas salmonicida occurred frequently in farm-raised Brachymystax lenok recently and Dوٴected the healthy development of cold-water fish aquaculture in China. In this study, the effect of a pathogenic strain A. salmonicida (LN1301) on four tissues (including liver, spleen, kidney and intestine) of fish was investigated. LN1301 was originally recovered from liver of diseased juvenile Brachymystax lenok with septicemia signs. $rtiÙ½ciDO infection proved that LN1301 was highly virulent to fish when challenged by wounded immersion or intraperitoneal injection. Healthy juvenile Brachymystax lenok (body weight of 90g-100g) were used for virulence assays and observation of histological changes. Нe experimental fish were randomly assigned into treatment group (n=3) and control group (n=3). Нe Ù½sh in the treatment group was intraperitoneal injected with LN1301 strain at a dosage of 1×106 CFU and the control fish received equal amounts of distilled water. Нe fish which exhibited clinical signs were then sDcrificed and the tissues were taken carefully and Ù½xed quickly into the Bouin’s solution for routine histological procedures. Нe results indicated that there were obvious histological changes in several tissues of LN1301 infected fish.