Abstract: A greenhouse experiment was conducted to assess the chamber effect on growth and nitrogen fixation in Sesbania aculeata (L.) at two levels each of soil salinity (electrical conductivity 4.65 and 7.23 dS m-1) and moisture (15 and 25%, v/w). The plants were grown either in the open or placed in an open-top polyethylene chamber and harvested 6 weeks after seed sowing. Salinization of soil led to a decrease, while higher moisture caused an increase, in different growth attributes of the plants. Growth reduction due to salt stress was less than that due to low moisture stress. Plants kept in the open-top polyethylene chamber showed better growth than those placed outside (in the open); all the parameters studied were better in the chamber. Chamber effect measured as Biomass Enhancement Ratio (BER) averaged 1.22 for different salinity and moisture treatments. However, root biomass of plants grown in the chamber was less than those grown in the open. Negative effect of salinity and low moisture was mitigated to a significant extent under chamber conditions. The analysis of root and shoot material for total N and 15N showed significant amounts of N2 being fixed as measured by isotopic dilution technique. Significantly higher amounts of N were fixed at 25 than 15% soil moisture; soil salinity had a depressing effect on the amount of N2 fixed. The contribution of biologically-fixed N (Ndfa) to the total N content of shoot and root portions was 23-62% and 21-52%, respectively, under different growth conditions. Contribution of Ndfa decreased with salinity but was more at 25% than 15% soil moisture.