Exploitation of small hydropower sources requires the use of small turbines that combine efficiency and economy which can conveniently cater the power needs of rural and small communities. Cross-flow turbines are used widely in such micro hydropower plants due to their simple design, easier maintenance, low initial investment and modest efficiency. Also, because of their suitability under low heads, their efficient operation under a wide range of flow variations and ease of fabrication, cross-flow turbines have been extensively employed. The primary objective of this study is to numerically analyze the characteristics and the fluid flow in a cross-flow hydro turbine and to optimize its performance by geometrically modifying the several parameters. During the process, a base model was chosen, the design was modified simultaneously by varying the nozzle shape, changing the guide vane angle, varying the number of runner blades and simulations were carried out individually. Two phase (air & water at 25 degrees C), steady state with SST turbulence model was selected in the commercial CFD code ANSYS CFX 13.0 for the numerical simulation. The design parameters included 10 m head, 0.1 m(3)/s flow rate and 642 rpm rotational speed. The results obtained showed that the best efficiency obtained from the base nozzle was 63.67% which was geometrically modified that improved the turbine performance and the efficiency reached 76.60% (increase by 12.93%). Velocity distribution, pressure contours, output torque within the flow domain were also characterized. It was observed that the re-circulating flow region was reduced and also its pattern was varied. (C) 2015 Elsevier Ltd. All rights reserved.