There are contrasting reports upon the level of effectiveness of motor imagery in learning new motor skills, but there is general consensus that motor imagery can lead to improvements in performance, especially in combination with physical practice. In the present study we examined the effectiveness of motor imagery in the acquisition of movement invariants in two grapho-motor trajectorial learning tasks with differing visuospatial components: 'Ideogram drawing' and 'connecting circles'. Two subject groups were studied: An imagery group, which underwent 10 min of motor imagery training and a control group, which practised a control visuomotor task over the same period of time. The results showed that imagery training alone enabled the subjects to achieve a significant approach to movement isochrony as well as a significant shifting of peak velocity toward the target. After a practice phase, both groups improved their performance, but the imagery group was still significantly faster than the control group. Furthermore, a series of tests measuring visual imagery abilities was administered to the subjects. There were however no significant relationships between the motor performance and the visual imagery ability levels of the subjects. It is concluded that motor imagery can improve the acquisition of the spatio-temporal patterns of grapho-motor trajectories and that there are different processes involved in visual and motor imagery.