Multiple sclerosis is believed to be triggered by the interplay between the environmental and genetic factors. In contrast to the Paleolithic diet, the modern Western diet is high in Na+ and low in K+. The present study was undertaken to determine whether high K+ intake alleviated experimental autoimmune encephalomyelitis (EAE), a model of multiple sclerosis. Treatment of C57BL/6 or SJL mice for 7 days with a 5 % K+ diet prior to induction of EAE and maintaining mice on the diet until the end of experiments delayed the onset, reduced the peak, and accelerated the recovery of EAE in both strains compared with mice on a control diet (0.7 % K+), whereas feeding C57BL/6 mice with a 0.1 % K+ diet did the opposite. High K+ intake increased the splenic Treg cell frequency in the pretreatment and peak EAE. Thus, high K+ intake attenuates EAE, possibly by increasing the Treg cells.