Abstract: The effect of [S] on the strength and toughness of low alloy steel plate in which sum of [P], [N], T[O] is less than 80×10^-6was investigated. It is found that the strength of the steel plate decreases with [S] increasing when it is less than 50×10^-6. And when [S] is more than 50×10^-6, the variation of [S] has no significant effect on the strength of steel plate. The ductile-brittle transition temperature drops and its difference between length direction and width direction reduces with decreasing [S] content of steel plate. However, even when [S] is reduced to 10×10^-6, the difference of ductile-brittle transition temperature is still 16 ℃.