The role of social capital in community collective action and public work participation was investigated featuring the land consolidation project in semiarid area, Arak District, Markazi Province, Iran. An intensive farm household survey was conducted to identify and measure the level of social capitals and their impacts on participation rate in collective action and land consolidation project. Logit regression analysis was applied to 177 household samples. Neither human capital (educational level) nor physical capital (land holding size) did not influence community activities participation. While physical capital has negative impact on land consolidation participation. It appears that the larger farmers, who already expanded their farm size through spontaneous land exchange with neighbor farmers, had little incentive to participate in land consolidation. Cognitive bonding social capital, measured by the degree of trust in community members, was significantly positive to participate in community collective actions, while not in land consolidation. Cognitive linking social capital, measured by the degree of farmers' trust in local government extension officer, was significantly positive on participation in land consolidation but not for community activities. Solidarity of community members was not significant for both cases. It is suggested that the trustful relationship between the individual local community members and government official is important to promote public works which require contribution from the beneficiaries.