The study determined the effect of Green River Project (GRP) on rural poverty alleviation in Bayelsa State, Nigeria. The objectives of the study were, first, to determine the differences in welfare indicators achieved by beneficiaries before and within participation in the GRP and secondly, to determine the problems encountered by beneficiaries in the Project. Data were elicited with the interview schedule which was randomly distributed to 90 direct beneficiaries of the Project. Analysis of data were achieved with frequencies, means, percentages, modified impact evaluation measuring model and Wilcoxon signed – rank test. Results revealed that out of the 26 poverty alleviation indicators studied, the Project performance was effective in 19. The effective performance were in net farm income, video machine, set of upholstery chairs, mobile telephone, canoe, engine boat, any four-wheeled vehicle and gathering of materials for building of block/zinc house. Others were opened bank account, opened fixed deposit account, purchased shares, participation in contribution (ntu), purchased land, farm size, sheep/goat size, fishpond number, membership in co-operative society, yield of wet cassava roots and yield of maize grains. Although the Project has shown evidence of poverty alleviation in the study area, but the test of hypothesis of the difference between poverty reduction indicators achieved before and within Project participation showed no significant difference [Z-cal (-0.88) < Z-tab (0.30)]. Insufficient storage facilities for farm products, inadequate market for farm products and inadequate supply of farm inputs by GRP were identified as problems contributing to this non-significant result. The study recommends the provision of adequate storage facilities and markets of farm products and the supply of enough farm inputs by GRP to beneficiaries to bring about significant result in rural poverty alleviation in Bayelsa State.