Moss colonies composed of two species Sanionia uncinata and Bryum pseudotriquetrum are abundant in the vicinity of Great Wall Station on King George Island. Vertical cross-sections of these colonies were examined to know the colony structure indicating the interaction between the two species. In several colonies, a layer composed of B. pseudotriquetrum was partially covered with shoots of S. uncinata (pattern 1). In some other colonies, a layer composed of S. uncinata was partially covered with shoots of B. pseudotriquetrum (pattern 2). For the rest of the colonies, both species coexisted without covering each other (pattern 3). It is concluded that the proportion of the two species in a colony has changed through the colony growth, but the direction of the change varies among the colonies at each site.