Abstract: The paper summarizes the development of the X60 and X65 seamless steel pipes for pipeline purpose,describes the determination of the steel chemical composition and the processes of on-line normalization and controlled-cooling for the pipe and discusess toughening mechanism of the steels. Relevant pilot commercial production has proven that with steel containing O. 16%C,l. 45%Mn, 0. 05%Nb and 0. 0l NV and the on-line normalization treatment, the X60 seamless steel tube can be obtained. Based on the said chemical complsition,the X65 pipe can also be made by means of addition of Cr in a small ammount,properly increasing Si content,prlperly controlling of N content and adopting on-line normalization treatment and controlled-cooling processes. Relevant operation practice has proven that the chemical composition selected and the processes em-ployed are adequate.