Abstract: This paper analyzes the effects of social influence and participation in collective action initiatives on soil conservation effort among smallholder farmers in Lake Naivasha basin, Kenya. We apply binary and ordered probit models in a two stage regression procedure to cross-sectional data collected through a household survey among randomly selected smallholder farmers. Smallholder farming systems in the research area are associated with practices that render farmlands susceptible to soil erosion causing negative impacts on land and the environment. Therefore, strategies that encourage soil conservation are likely to also offer solutions for dealing with agri-environmental challenges and poverty alleviation. Results indicate that social capital facilitates participation in collective action initiatives which then influence individual soil conservation efforts. Neighborhood social influences, subjective norms, gender, education level, farm size, access to credit and livestock ownership also emerge as key determinants of soil conservation effort. Policy implications drawn by this study encourage strategies to increase participation and effectiveness in collective action initiatives as a boost to soil conservation. Implementation of soil conservation practices could also be encouraged through awareness increasing instruments, facilitating access to agricultural micro-credit and paying attention to gender related challenges on knowledge access and rights over land and other natural resources. [Copyright &y& Elsevier]