This ethnographic study examined socio-cultural factors which affect on 5-year-old children\'s block play and the characteristics of peer interaction. The results are as follows. The block play was deeply related to the children\'s daily life. Using internet, young children found resources related to the block play and applied to the play, playing TV animations, constructing the play with the themes related to family life, and expanding the experience of community in the block play. The characteristics of peer interaction in the block play were \'sharing\', \'collaboration\', and \'conflict.\' During block play, first, young children shared not only play area and play materials, but also \'emotion\', ‘themes\', \'language\', \'play script\', and ‘rules’ during the block play. Second, young children collaborated to build the construction together or to solve the problems in the course of discussion. Finally, young children experienced conflicts as they participated in the block play, shared the blocks with peers, or communicated each other during the block play.