A flow injection (FI) method is described for the determination of pirimicarb. It was found that an enhanced chemiluminescence (CL) signal is obtained when employing the luminol-H2O2-horseradish peroxidase (HRP) system. Under the optimum experimental conditions, the enhanced CL intensity was linear with the concentration 4.25-30.75 ng mL-1 (r = 0.997, n = 8) with a relative standard deviation of 0.99%, containing 12.75 ng mL-1 (n = 8). The limit of detection of the investigated compound was 0.12 ng mL-1. The method shows a moderate selectivity against other pesticides (Amitrole, Atrazine, 2,4,5-T, Dichlorprop, and Metamidophos).The proposed method was sensitive, simple, rapid, and successfully applied to the determination of pirimicarb when it is applied in freshwater; the mean recoveries were 98.3-118.5%.