It has been suggested that motor planning involves internal movement simulation or motor imagery. Previous studies indicate that predicting action consequences involves motor imagery, and motor imagery contributes heavily to movement planning. The present experiment studied the influence of grasping habits and end-state comfort on the imagery of possible and impossible manual action sequences. Thirty participants were simultaneously presented with two images. The left image depicted the start posture of a right hand when grasping a hammer, while the right image depicted the end posture in which the hammer was gripped in different grasping habits (habitual/non-habitual) and end postures (comfortable/uncomfortable). The hammer in the right image was always in a vertical orientation, while the hammer in the left image was rotated in the picture plane in steps of 45°. Moreover, the two images combined showed either a physically possible or physically impossible action sequence, and participants were asked to judge whether the two images were from the same movement or not. Results showed that participants made fewer errors and faster reactions with the habitual than the non-habitual grips in possible action sequences (all ts > 5.94, all ps < 0.001) but not in impossible sequences (all ts < 0.415, all n.s.). No significant difference was found between the comfortable and uncomfortable end postures in both action sequences (all Fs < 3.48, all n.s.). These findings suggest that grasping habits seem to outweigh biomechanical constraints (i.e., end-state comfort) in motor imagery of manual action sequences.