Heterogeneous enantioselective catalysts based on nickel, tartaric acid and NaBr supported on activated carbon or graphite were characterized and tested in the asymmetric hydrogenation of methyl acetoacetate (MAA). Nickel crystallite size depended on the type of carbon support, the preparation conditions and reduction temperature of nickel. Enantioselectivity increased significantly with increasing nickel crystallite size. High nickel loading (up to 85wt.%) and large crystal size (<5000 angstroms) were examined. Operating conditions such as temperature, hydrogen pressure and catalyst to substrate ratio were varied over a wide range to achieve high enantiomeric excess values. Enantiomeric excess as high as 91% was obtained with nickel on graphite.