Abstract: Masjid-I-Sulaiman (MIS) (Khozestan province, South-West of Iran) is contaminated with subsurface of natural sour gas leakage. In the present report the possible effect of environmentally contamination with natural sour gas on mortality due to cancers and psychiatric disorders was investigated. Data concerning mortality in MIS and Khozestan province are compiled using reports from the Statistical Center of Khozestan province from 20th March 2000 to 19th March 2002. The mortality in the Izeh and Shoshtar, the nearest city to MIS and the Khozestan province (excluding MIS) were used as controls. To test the null hypothesis that the mortalities due to cancers and psychiatric disorders in MIS are equal to the control populations, the Chi-square test was used. Statistical analysis of data demonstrated that there were significant differences between MIS and Khozestan province for cancers (χ2 = 20.58, df = 1, p<0.00001) and psychiatric disorders (χ2 = 43.79, df = 1, p<0.00001) related mortalities. There were significant differences between MIS and Izeh for cancers (χ2 = 7.24, df = 1, p = 0.0071) and psychiatric disorders (χ2 = 17.88, df = 1, p = 0.00002) related mortalities. Also there were significant differences between MIS and Shoshtar for cancers (χ2 = 9.23, df = 1, p = 0.0023) and psychiatric disorders (χ2 = 9.80, df = 1, p = 0.0017) related mortalities. There was no difference between either Izeh or Shoshtar and Khozestan province for mortalities due to cancers and psychiatric disorders. Taken together, it is suggested that high level of sulfur compounds in MIS has some role(s) in the high mortality rates due to cancers and psychiatric disorders in MIS.