Kenya has got a rapidly increasing population which was estimated to be 36 million in the year 2009 with a growth rate of 2.7 per annum hence the need for diversified food production. Water deficit is one of the most environmental stresses affecting agriculture productivity. Drought may affect crop yield and gas exchange at any developmental stage while early reproductive stage is found to be one of the most susceptible phases of a crop to drought stress. NERICA (New Rice for Africa) are high yielding rainfed rice varieties with early maturity and has shown high potential to revolutionize rice farming even in Africa’s stress afflicted ecologies. However, NERICA varieties vary in their response to water deficit. A pot experiment was conducted in 2009 at the Maseno University Botanic garden, to evaluate the responses of five NERICA varieties (NERICA1, NERICA 2, NERICA 3, NERICA 4 and NERICA 5) to water deficit during their vegetative or reproductive stage of their development. The response pattern of crop yield and gas exchange parameters to water deficit imposed at different growth stages might provide basis for selecting the most tolerant variety to water deficit in order to stabilize yield and solve food crisis. The treatments were; T1- irrigating the pots with a litre of water after every two days (Control), T2 -water deficit at vegetative stage in which water was withheld by irrigating the plants using one litre of water after every six days from 30-50 days after planting; T3-water deficit at reproductive stage in which water was withheld by irrigating the plants using one litre of water after every six days from 51-71 days after planting. Water deficit caused a significant reduction in gas exchange parameters and yield more at the reproductive stage as compared to water deficit at vegetative stage. The results indicate that NERICA 2 and 4 were tolerant as compared to NERICA 1, 3 and 5 to water deficit occurring at vegetative stage or reproductive stage because