A threaded connection for steel pipe with improved sealing performance is provided. A threaded connection (1) for steel pipe includes a pin (10) and a box (20). The outer diameter of the box (20) is smaller than 108% of the outer diameter of a steel-pipe body (30). The pin (10) includes a pin lip (12) including a first seal surface (11), a male thread (13) constituted by a single-stage tapered thread, and a second seal surface (14). The box (20) includes a first seal surface (21), a female thread (23) constituted by a single-stage tapered thread, and a box lip (22) including a second seal surface (24). When assembled, the first seal surfaces (11, 21) are in contact with each other and the second seal surfaces (14, 24) are in contact with each other. A portion of the male thread (13) located near the end thereof close to the pin lip (12) includes a plurality of thread root surfaces extending parallel to the pipe axis (CL) and having the same diameter. A portion of the female thread (23) located near the end thereof close to the box lip (22) includes a plurality of thread root surfaces extending parallel to the pipe axis (CL) and having the same diameter.