Abstract: Since the construction of early industrial pipelines, construction of the oil/gas pipelines has been developed for more than one century. And from 1928 the first edition of the specification of API Spec 5L for Linepipe was issued up to 2007 the 44th edition came to be publicized, it has been nearly eight decades for development thereof. Thanks to continual amendments and revisions, the specification has been a prevailing international standard as used for steel linepipes for oil/gas transport pipeline service. The 44th edition of API Spec 5L was issued on October 1, 2007, and became effective on October 1, 2008, being jointly publicized with ISO 3183: 2007 (the 2nd edition) as the equivalent thereto for the first time. Described in the paper is the development course of API Spec 5L as well as the latest development and changes of it.