The strength of polycrystalline materials increases with decreasing grain size. The increase of strength is usually associated with deterioration of ductility, especially for materials having sub-micrometer or nanometer in grain size. It has bee suggested that the ductility of submicro- or nano- grained materials can be improved significantly by introducing a bimodal distribution of grain sizes. The purpose of the present study aims at clarifying the microstructural parameters of the bimodal distribution, such as area ratio and size difference, on the strength and ductility of pure nickel and nickel-cobalt specimens produced by electrodeposition. The microstructural parameters were determined from orientation imaging mapping technique using electron backscatter diffraction. Results indicated that the yield strength is mainly determined by the average size of the fine grains, whereas the tensile strength has a good relation with the average grain size in total. Moreover, it was showed that samples having a area ratio of the fine grains lower than 30% or higher than 70% possess a better ductility. The possible mechanism is discussed in detail.