Abstract: A portable boat seat for releasable attachment to a transverse boat thwart or any like horizontal supporting structure having opposing edges. A seat member is attached to a main frame by a turntable for rotation about a substantially vertical axis relative to the main frame and a supporting thwart. The main frame includes a pair of parallel, spaced apart longitudinal channel members to the upper surface of which is attached the turntable. Secured transversely across an end portion of the channel members is a first grasping member. A second and opposing grasping member is secured to a pair of slide members slidably engaging the channel members for relative longitudinal sliding movement. A coil spring biases the grasping members toward each other. Extension of the main frame against the spring permits the grasping members to be positioned adjacent and outside the opposing edges of the thwart.