This study integrated collaborative problem-based learning (collaborative PBL) with blended learning to explore the emerging process and function of online learning communities among preservice teachers. Thirty-two preservice teachers participated in a 16-week instruction program. Analyses of online group discussions and portfolios found that (a) the integrated approach facilitated the preservice teachers' formation of online learning communities; (b) the preservice teachers' online learning communities emerged via four stages: motivation and acquaintance, socialization and belongingness, information exchange and consensus, and tacit understanding and development; and (c) six factors influenced the development of the preservice teachers' online learning communities. (Contains 3 figures and 3 tables.)