The experiment was conducted to investigate the effects of cobalt (Co) and copper (Cu) supplementation on vitamin B₁₂ status and blood parameters in lambs. Sixteen lambs were assigned randomly to control group which was fed with the basal diet containing 0.086 mg Co/kg DM and 6.09 mg Cu/kg DM and the Co-, Cu- and Co-Cu groups, supplementation of 0.03 mg Co/kg DM and 10 mg Cu/kg DM, separately and in combination to the control diet. The Co- and Co-Cu supplemented lambs showed higher vitamin B₁₂ concentrations in both ruminal fluid and plasma, and lower methylmalonic acid in plasma compared with other groups (P<0.01). No difference was observed in plasma glucose between treatments (P>0.05). Haeme-depending blood parameters were enhanced by Co or Cu supplementation. It was concluded that vitamin B₁₂ production by rumen microorganism was accounted for by cobalt intake with no collaborate effects of Co plus Cu supplied in the diet. Co or Cu supplementation has positive effects on blood parameters.