Osteoporosis and its related fractures are major public health concerns. Physical activity (PA) is crucial for bone density preservation and fractures prevention. Yet, gaps in understanding exist regarding how ethno-cultural backgrounds might shape attitudes, intentions and actual PA participation. Based on the theory of planned behaviour (TPB) for predicting PA, the aims of this study were: (i) to compare attitudes, subjective norms, perceived control, intentions and knowledge, across four ethno-cultural groups; (ii) to evaluate the fit of the model we constructed across four ethno-cultural groups of women: Israeli-born Jews and Israeli-born Bedouin-Muslims, immigrants from the Former Soviet Union (FSU) and Ethiopian immigrants. Four hundred women (one hundred from each group), aged >65, completed valid and reliable questionnaires assessing knowledge, TPB components and actual PA. The level of knowledge on osteoporosis was relatively low among all four ethno-cultural groups. Intention to participate in PA was the only variable that directly predicted actual PA. Intention to participate in PA served as a mediator among attitudes, subjective norms, perceived control and actual PA. The structural equation models (SEMs) revealed that among Israeli-born Jews and Ethiopian immigrants, TPB components mediated the link between knowledge and intention to participate in PA. Among FSU immigrants and Israeli Bedouin-Muslims, the knowledge variable was not included in the final model, as its contribution was not significant. It is essential to better understand and augment interventions that enhance PA in the community, and to address the unique needs of each ethno-cultural group.© The Author(s) 2020. Published by Oxford University Press. All rights reserved. For permissions, please email: firstname.lastname@example.org.