To achieve secreted expression of the truncated capsid protein from porcine circovirus type 2 (PCV2) in Pichia pastoris. RESULTS: A truncated cap gene (tcap) with a deleted N-terminal nuclear localization signal was optimized and synthesized. Effective secreted expression was achieved in P. pastoris GS115. The high-productive recombinant strain for tCap was grown in a 5 l bioreactor and the productivity of tCap in supernatant reached 250 μg/ml. Furthermore, serum antibody test demonstrated that adjuvant-assisting tCap induced a significant increase of specific PCV2-Cap antibody over time in mice and a similar antibody level in pigs compared with a commercial Cap-based subunit vaccine. CONCLUSION: This work establishes a secreted expression strategy in P. pastoris for the production of PCV2 Cap with superior bioactivity, and this strategy might provide potential uses in developing Cap-based subunit vaccine in the future.