Dissertation (MSc Chemistry)The aim of this study was to determine the concentrations of hydrogen cyanide in different cassava varieties from four districts of two regions namely Tanga and Mtwara and to determine how Senna singueana leaf extract reduce the amount of hydrogen cyanide in the selected samples at different temperatures of 26 °C and 36 °C. From each district most cultivated variety of cassava sample was collected in the particular area. Titrimetric method was used to determine free hydrogen cyanide in it. The concentration of hydrogen cyanide was also estimated by the measurement of pH. In Tanga region, the highest mean concentration of hydrogen cyanide was found in a variety called Dide, cultivated at Mlola village in Lushoto district with 28.466 mg/kg while the lowest concentration of hydrogen cyanide 6.27 mg/kg was found in the cassava sample called Msufi which was found in Korogwe district. In Mtwara region, the samples collected at Kidumbe Mtoni Village, Newala district had the highest concentration of 35.1 mg/kg in a variety called Sumu ya panya while lowest concentration of hydrogen cyanide was found in the cassava sample called Mnalikuchumbani with the mean concentration of 0.5 mg/kg. The percentage reduction in concentration of hydrogen cyanide in cassava after treatment with Senna singueana leaves extracts of ethanol, water, acetone and mixture was 40.9, 34.30, 29.13 and 22.86, respectively. The results showed that the treatment is efficient at 36 °C than at 26 °C. This study showed that the leaf extracts of Senna singueana can be used to treat the cassava inorder to reduce the concentrationsof hydrogen cyanide.