In order to determine whether foals of move dominant mothers were harassed less by mares than those of lower-ranked mothers, harassment of foals was studied in a herd of Jeju ponies (Equus caballus) consisting of 73 mares, their 53 foals, and one stallion. Mares Harassed the foals on 71 occasions between March to September,1998. The frequency of harassment tended to decrease as foals aged, but the relationship was not significant (P = 0.079). Foals were harassed when sleeping (n = 14), grazing (n = 19), moving (n = 8), approaching a mare in the vicinity (n = 13), or play-fighting with the foal of the harassing mare (n = 17). Mares harassed foals of younger, more subordinate mares than those of older, more dominant mares (P < 0.001). We conclude that early social experience of foals is associated with the dominance rank of its mother.