Objective : To determine the prevalence of Thiamin deficiency in Thai congestive heart failure (CHF) patients. Methods : Blood sample were taken from patients who were admitted to King Chulalongkorn Memorial Hospital with the diagnosis of CHF and examined for TPPE (Thiamin-pyrophosphate Effect) and ETK AC (Activation Coefficient of Erythrocyte transketolase Activity), to determine the prevalence of Thiamin deficiency. Patients were interviewed and detailed medical records were collected to identify risk factors for Thiamin deficiency. Results : Out of 99 consecutive patients with CHF. 15 patients (15.2%) had ETK AC>1.15. Among these, 7 patients (7.1%) were classified as having mild Thiamin deficiency (ETK AC 1.15-1.20) and 8 patients (8.1%) were classified as having marked thiamin deficiency (ETK AC>1.20). Age, gender, ejection fraction, etiology of CHF, duration of CHF, history of diuretic use were not found to be associated with Thiamin deficiency. Alcoholic consumption and low socioeconomic status were found to be associated with Thiamin deficiency. Conclusion : The prevalence of thiamin deficiency in Thai CHF patients was 15.2%. Alcoholic consumption and low socioeconomic status were the two risk factors for this condition.