Objective Based on the specific binding of target with aptamer, a portable aptasensor combined with highly sensitive electrochemical methods was designed to complete the rapid detection of biological toxins Okadaic acid (OA) in shellfish. Results A simple aptasensor based on screen-printed carbon electrode (SPCE) with modification of chitosan (CS) and gold nanoparticles (AuNPs) was designed for electrochemical determination of OA, and the electrode surface was modified with AuNPs by potential-sweeping electrodeposition, which greatly improved the electrochemical response. The entire detection and characterization process were carried out by cyclic voltammetry (CV) with a linear correlation in the range from 0.01 ng/mL to 100 ng/mL and a LOD of 6.7 pg/mL. Furthermore, a recovery rate of 92.30-115.98% was obtained demonstrating excellent accuracy through the recovery trial of mussel and scallop samples. Conclusion The current method based the change of spatial structure before and after aptamer binding target showed great potential in rapid on-site and low-cost detection of OA for its simplicity.