To clone and express an important cashew nut allergen Ana o 3 in Escherichia coli (E.coli) using pCold-SUMO expression vector and identify its immunocompetence.Methods Total RNA was extracted from the cashew nut and reverse transcribed into cDNA. Then, the full-length cDNA sequence of Ana o 3 was amplified by nested polymerase chain reaction (PCR) using specific primers, and subsequently inserted into the pCold-SUMO expression vector between StuⅠand BamHⅠ restriction sites. The correct construct was identified by both colony PCR and gene sequencing. The inducible expression of Ana o 3 was performed at 15 ℃ by an addition of L-+-arabinose and isopropyl b-d-thiogalactoside (IPTG), and the purification of the recombinant His-tagged protein was accomplished by the Ni-NTA purification system. The immunocompetence of the recombinant Ana o 3 was evaluated by Western blot. Results DNA sequencing analysis showed that the full length of Ana o 3 was 417 bp, encoding a polypeptide of 138 amino acids which was in accordance with that in withGenBank. Also, the sodium dodecyl sulfate polyacrylamide gel electrophoresis result indicated the molecular weight of the recombinant Ana o 3 was 27 kD, which was in agreement with the theoretical value. Additionally, Western blot results showed that the recombinant Ana o 3 had good reactivity with 13 cases of cashew-allergic serum samples.Conclusion A recombinant expression vector of Ana o 3 had been successfully constructed, and the purified recombinant protein exhibited good reactivity with cashew-allergic sera.