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　250°C,　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　300°C.　The　DSC　curve　obtained　at　20　K·min-1　heating　rate　showed　low　energy　exotherm　beginning　at　300°C　and　continuing　to　350°C　at　which　point　the　main　thermal　release　occurred,　reaching　peak　differential　heat　flow　at　372°C,　the　release　ΔH　was　14.22　J·g-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.