Strains of Pseudomonas syringae pv. syringae (Pss) were isolated from P. armeniaca in different geographic areas in East Azerbaijan province, Iran, and studied for genetic diversity and host preference. Results of morphological, physiological and biochemical tests showed no differences among strains and syrB gene was determined to be present in all strains by PCR using gene-specific primers. Results of antibiotic assays showed that all strains were resistant to ceftriaxone and erythromycin, while tetracycline induced the strongest growth inhibition. In pathogenicity tests, all strains incited progressive necrotic lesions on apricot twigs at inoculated sites. Severity of symptoms was variable on mango leaves, lemon fruits, bean pods and tomato seedlings. To assess genetic diversity among strains, clustering of strains was performed based on partial sequences of the 16S rRNA and the rpoD housekeeping genes and DNA fingerprinting using IS50-PCR analysis. Cluster analysis was performed using the Unweighted Pair Group Method with Arithmetic (UPGMA) method and Jaccard's similarity coefficients. High genetic diversity was detected among strains. All Pss strains were divided into two distinct clusters at the 37% similarity level. In summary, this study indicates that Pss strains isolated from apricot in East Azerbaijan province in Iran, are genetically diverse, do not display host specificity, but are heterogeneous in regard to aggressiveness.