Motor imagery (MI) and action observation (AO) are cognitive motor processes. Previous studies have examined themodulation of corticospinal excitability, spinal reflex excitability, and cortical activity during MI and AO. However, howthe cortical network changes during these processes were still unknown. Here, this study investigated the cortical networkchanges during MI, AO, and MI combined with AO (MI+AO) by analyzing changes of phase relations (phase synchronyanalysis). 64-ch electroencephalographic signals were recorded from twelve healthy males while they were performingMI, AO, and MI+AO of walking. In our results, phase desynchronization occurred between the sensorimotor areas andthe visual areas during AO and MI+AO, while MI by itself did not cause phase desynchronization. These results suggestthat AO changes cortical connectivity between the sensorimotor and visual areas while the cortical connectivity staysduring MI. These findings have implications for understanding the cortical network changes induced by cognitive motorprocesses.