Whether common marmosets (Callithrix jacchus) exhibit spontaneous alternation behavior was examined. Marmosets were allowed to explore one of the two arms of a Y-shaped maze, and after delays of various lengths, their preference to enter the previously entered or alternate arms was examined. The marmosets showed spontaneous alternation behavior; they preferred to enter the alternate arm after a delay of 2 hours or shorter, but such a preference was lost after a 24-hr delay. The loss of the alternation with longer delay can be discussed in terms of marmosets' foraging strategies. When the visual cue at the entered arm was changed after the initial exploration, the marmosets did not exhibit spontaneous alternation, suggesting that the visual cue had some role in the alternation behavior. Spontaneous alternation behavior in marmosets will provide an opportunity to simply measure their memory without providing specific task training.