Dioxin is still long persistent in environment. The effect of Dioxin on thyroid function is inconsistent. Da Nang and Bien Hoa airbases have been hot spots for persistent contamination since 1961. Inhabitant living around these sites has been exposed to dioxin for a long time. Serum dioxin level of people was much higher than those in other sites. This study evaluates serum dioxin level using DR CALUX and thyroid function including T3, T4, FT3, FT4, TSH measurement. T3 level was found association with serum dioxin level. There were not any relation between T4, FT3, FT4 and TSH and dioxin level.