This paper discusses the learning mechanism enhanced by communities of practice (CoPs). It uses the case of Japanese nursing homes practicing SAIDO-learning. CoPs are defined as ‘groups of people who share concern, a set of problems, or passion about a topic, and who deepen their knowledge and expertise in this area by interacting on an ongoing basis’ (Wenger, McDermott & Snyder, 2002, p. 4). Two learning mechanisms of CoPs are suggested. One is derived from the difference between organizational canonical view and non-canonical view in CoPs. The other is facilitated by boundary crossing. This paper presents a study that investigated learning from non-canonical view, and boundary crossings facilitated by establishing CoPs within, between, and across organizations related to nursing homes. The study addressed the following research question: ‘How do CoPs enhance organizational boundary crossing and facilitate learning?’ This study found that nursing homes achieved boundary crossing through CoPs spontaneously established at nursing home facilities. Staff members established the CoPs to learn about SAIDO-learning, which further motivated them to learn, while they formed CoPs by practising to lead non-canonical view. One remarkable aspect was the establishment of ‘advanced CoPs’, which involves several CoPs and allows boundary crossing among CoPs. Then, larger advanced CoPs are developed through them in a nested structure. This multi-layered structure of advanced CoPs facilitates staff members' spontaneous learning through boundary crossing. Moreover, the structure stimulates people who are not CoP members to establish CoPs and encourages members to establish advanced CoPs for crossing the boundaries between CoPs. Further discussion and theoretical and practical implications are proposed.