Based　on　a　unique　method　to　synthesize　WC-Co　composite　powder　by　in-situ　reactions　of　metal　oxides　and　carbon,　the　effects　of　the　carbon　addition　in　the　initial　powders　on　the　phase　constitution,　microstructure　and　mechanical　properties　of　the　cemented　carbides　were　investigated.　It　is　found　that　with　a　suitable　carbon　addition　the　pure　phase　constitution　can　be　obtained　in　the　sintered　bulk　from　the　composite　powder.　The　mechanical　properties　of　the　cemented　carbides　depend　on　the　phase　constitution　and　the　WC　grain　structure.　To　obtain　the　excellent　properties　of　the　WC-Co　bulk,　it　is　important　to　obtain　the　pure　phase　constitution　from　the　appropriate　carbon　addition　in　the　initial　powders　and　a　suitable　grain　size.