Pressures on protected areas (PAs) in Tanzania are increasing through the extractive use by surrounding communities. Understanding how environmental reliance varies in relation to distance from PAs and in relation to household’s socio-economic characteristics is important for PAs management and decision of poverty alleviation strategies. This study therefore aimed to quantifying the reliance on cash environmental income as a share in total household income over a gradient of distance from PA boundaries in Western Serengeti and evaluates how it is influenced by socio-economic characteristics. Data was collected through a semi-structured questionnaire of 150 households, randomly selected in three villages. Results indicate that environmental cash-income varies from 21.3% to 45.2% of the total annual cash-income, representing on average 37.8% of the total annual cash-income of all households surveyed. Households closest to the boundary of Serengeti National Park (SNP) are relatively more reliant on environmental income than those located relatively far. Environmental cash-income reliance is associated with household socio-economic factors including distance from SNP boundary, household wealth rank and absolute income from off-farm activities. The main sources of environmental cash-income are fuel-wood, construction materials and wild foods. Reducing environmental reliance requires promotion of off-farm activities, improved wood fuel stoves electricity and alternative sources of fuels.