A steel pipe with excellent expandability, comprising, by mass %, C: 0.1 to 0.45%, Si: 0.3 to 3.5%, Mn: 0.5 to 5%, P: less than or equal to 0.03%, S: less than or equal to 0.01%, soluble Al: 0.01 to 0.8% (more than or equal to 0.1% in case Si content is less than 1.5%), N: less than or equal to 0.05%, O: less than or equal to 0.01%, and balance being Fe and impurities, having a mixed microstructure comprising ferrite and one or more selected from fine pearlite, bainite and martensite, and having a tensile strength of more than or equal to 600 MPa and a uniform elongation satisfying following formula (1).This steel pipe, having the above described chemical composition, can be obtained, for example, by being heated at temperatures from 700 to 790° C., then being forced-cooled down to a temperature of lower than or equal to 100° C. with the cooling rate of greater than or equal to 100° C./min at the temperature from 700 to 500° C. u-el≧28−0.0075TS  (1), wherein u-el means uniform elongation (%), and TS means tensile strength (MPa).