Objective: Organophosphate poisoning is a serious clinical entity and of considerable morbidity and mortality. Several factors have been identified to predict outcomes of organophosphate poisoning. This investigation aims to identify the relationship between the dynamics of serum cholinesterase (SChE) activity and mortality. Methods: In this retrospective study, medical records of all patients with acute organophosphate poisoning were reviewed from January 2001 to December 2009. Clinical features, SChE activity, Glasgow Coma Scale, laboratory findings, electrocardiogram finding, management and their outcomes were examined. Results: A total of 169 patients were included in this study. A total of 55 patients were enrolled. Deceased patients were 8 in number. Absence of an increase in SChE activity was related with mortality in organophosphate poisoned patients (p value=0.036; odds ratio, 5.445; 95% confidence interval, 1.121-26.551). Conclusions: The absence of an increase in SChE activity is associated with higher mortality in organophosphate poisoning. The SChE dynamic activity can provide a guide to physicians in the evaluation and management of organophosphate poisoned patients.