This paper describes the "practice architectures"; and "ecologies of practice" of LS (lesson study) in an Indonesian private elementary school. It aims at drawing on LS as a form of professional learning from the perspective of contemporary practice theory (Kemmis, Wilkinson, Hardy, & Edwards-Groves, 2009; Kemmis, 2009a, 2009b). This case study discusses the distinctive features of LS as social practice at that school. Firstly, the author highlights the context of LS activity (January-June, 2010), as a part of School Improvement Program, which aims to develop participating teachers' capacities, i.e., teacher learning, by studying the nature of teaching and learning processes. Aligned with school's vision to develop a learning community, the program developed three main activities: (1) Leadership for Learning workshop that focused on exploring the nature of learning and teaching and the role of teacher in LS practice; (2) LS workshops that involved a "Plan-Do-See" cycle for designing, implementing, and reflecting upon teaching and learning activities; and (3) School Forum in which the participants shared experiences with other fellow teachers. Data were collected through focused group discussion, field observation, and document study. Secondly, the author discusses the practice architecture to describe distinctive"sayings", "doings", and "relatings" characteristics of LS practice in terms of interconnected "meta-practices" of learning community, leadership, and teacher learning. Finally, the paper argues, following Kemmis' works, that those meta-practices are mutually interdependent within ecologies of LS practice, which influence and are influenced by each other. (Contains 3 tables.)