Herein, we have designed a special strategy for detection of the important neurotransmitter serotonin by coupling the electrodeposition of serotonin oxidative products with the adsorption-controlled anodic electrochemiluminescent dynamics of the CdSe–triethylamine system. The stable electrochemiluminescent emission is found to decline in the presence of serotonin. This uncommon inhibition is attributed to the gradual accumulation of the electropolymerized serotonin products, which decrease the adsorbance of CdSe nanoparticles on the glass carbon electrode, as demonstrated by the scanning electron microscopic images (SEM) and the stripping voltammetric identification. Based on the inhibition effect, a facile strategy has been developed to sensitively detect the serotonin ranging from 0.2–10 μM, with a detection limit of 0.1 μM. The interference from the common species including ascorbic acid and uric acid has been investigated. The recovery rates in the spiked serum samples range from 94–112 %, thereby implicating its potential applications in the complex bioassays.