Canker is one of the most important diseases of stone fruit trees in the world and especially in Iran. Regarding its control problems using antibiotics and also because chemical methods are harmful to the health of consumers and cause resistance in pathogens, biological control can be used as an beneficial alternative to plant protection. In this study, in order to isolate the antagonistic bacteria and the disease agent, healthy and infected tissues of the fruit trees of the plum, peach, nectarine, almond, sweet cherry and sour cherry were sampled from the East and the West of Iran. The surfaces of the branches were washed and by the use of serial dilutions the bacteria were isolated on the KB medium. The isolates that produced fluorescence light under UV were selected and purified. For selected Pseudomonas syringae from infected tissues which were identified by LOPAT tests, pathogenicity were studied. 250 isolates detected from healthy samples were tested against infectious bacteria identified from infected samples. In order to study the effect of these antagonists against the pathogenic bacteria, a growth inhibitor (antibiosis) and antibiotic production (chloroform test) were used. 28 isolates with inhibitory halo against the causative agent of canker were identified by physiological, biochemical and morphological tests. All of these isolates were belonged to the P. fluorescens species. To investigate the effect of antagonists on preventing growth of the pathogenic agent in living conditions, tests were carried out on plum blossom trees. Analysis of data showed that the antagonistic treatments successfully prevented the blossom blast, so that the treatments reduced the incidence of disease from 64.7 to 89.6%. These findings showed that 10 isolates were successful in controlling the disease both in vitro and in vivo conditions.