Some microbial-associated molecular patterns (MAMPs), like glucan oligosaccharides, can be recognized by pattern recognition receptors (PRRs) of plant to elicit further immunity response. In this study, a novel glycoside hydrolase family 55 beta-1,3-glucanase (AcGluA) from Archangium sp. strain AC19 was cloned and expressed in Escherichia coli. Among the reported beta-1, 3-glucanases from the glycoside hydrolase 55 family, the purified AcGluA exhibited the highest activity on laminarin at pH 6.0 and 60 degrees C with 112.3 U/mg. Activity of AcGluA was stable in the range of pH 4.0-9.0 and at temperatures below 60 degrees C. The K-m and V-max of AcGluA for laminarin were 3.5 mg/ml and 263.5 mu mol/(ml.min). AcGluA hydrolyzed laminarin into a series of oligosaccharides, suggesting it was an endo-beta-1,3-glucanase. The high dose of oligosaccharides (1600 mg/l) had conspicuous biocontrol efficacy on the defense of rice seedlings to Magnaporthe oryzae, which provided a new idea for the development of green biopesticide.