Burning mosquito coils indoors generates smoke that can effectively repel mosquitoes. This practice is currently used in millions of households in Asia, Africa and South America.  However, the smoke may contain pollutants of health concern. This study is conducted to characterize the emissions from four types of widely used mosquito coils, two from China and two from Malaysia. All experiments were conducted in a well-mixed plastic chamber with a volume of 0.15 m³.  The results show that the smoke contained large numbers of ultra-fine (0.01 – 0.1 mm) and fine (0.1 –1 mm) particles. The emission rates of PM_2.5 were 62.79±3.01 mg/hr, 85.04±8.64 mg/hr, 116.52±14.12mg/hr and 114.80±11.61 mg/hr for these 4 types of mosquito coils respectively. The emission rates of formaldehyde and acrolein were in the ranges of 1434-7515 mg/hr and 165-1562 mg/hr, respectively.  Under the same combustion condition, the Malaysian mosquito coils generated more particles and aldehydes than the Chinese mosquito coils.  We applied these measured emission rates to predict exposures under realistic room conditions and found that such exposures can pose significant acute and chronic health risks.