Microstructures　and　composition　of　nanocrystalline　Ni-Co　alloy　produced　by　pulse　electrodeposition　were　studied　by　XRD　and　EDS.　The　microhardness　of　nanocrystalline　Ni-Co　alloy　annealed　at　various　temperatures　was　measured　and　the　thermal　stability　of　Ni-23.5%Co　(mass　fraction)　alloy　was　studied　extensively.　The　results　indicated　that　microhardness　of　Ni-Co　alloys　increased　slightly　after　annealing　at　low　temperatures,　and　reached　the　maximum　at　250C,　then　decreased　with　the　increasing　of　the　annealing　temperatures.　The　grain　size　of　Ni-23.5%Co　alloy　increased　from　13.5　nm　to　98.5　nm　when　the　annealing　temperature　rose　to　300C.　The　DSC　curve　obtained　at　20　Kmin-1　heating　rate　showed　low　energy　exotherm　beginning　at　300C　and　continuing　to　350C　at　which　point　the　main　thermal　release　occurred,　reaching　peak　differential　heat　flow　at　372C,　the　release　ΔH　was　14.22　Jg-1.　According　to　the　Kissinger　equation,　the　activation　energy　for　grain　growth　of　Ni-23.5%Co　alloy　was　calculated　to　be　212.5　kJ/mol.