A novel dual-coreactants electrochemiluminescent (ECL) immunosensor based on CdS-MoS 2 nanocomposites was designed for detection of procalcitonin (PCT). The CdS-MoS 2 nanocomposites were synthesized through a simple one-pot hydrothermal method, and served as highly efficient luminescent material for the ECL immunosensor. In addition, we used H 2 O 2 and K 2 S 2 O 8 as dualcoreactants, generating stronger ECL emission than that of K 2 S 2 O 8 or H 2 O 2 as an individual coreactant, which could improve sensitivity of the immunosensor. Under optimum conditions, the ECL assay for PCT detection was developed with excellent sensitivity of a concentration variation from 0.0001 to 10 ng mL −1 and limit of detection down to 33 fg mL −1 (RSD = 0.10). Additionally, the proposed immunosensor showed high specificity, good reproducibility, and long-term stability.