The addition of carbon changes Ms, Hkeff and Hc(perp) of sputter-deposited CoCr films: Ms is always increased, while Hkeff and Hc(perp) are either increased or decreased by the addition of up to 0.32 at% carbon. How the substrate temperature and the Cr content in the film influence the effect of added carbon is investigated. Higher substrate temperature tends to stimulate the increase in Ms caused by the addition of carbon. A higher substrate temperature and higher Cr content tend to stimulate the increase in Hkeff and Hc(perp) and to prevent the decrease in Hkeff and Hc(perp) caused by the addition of carbon. The increase in Ms with the addition of carbon seems to be caused by an increase in the degree of compositional segregation. The increase and decrease in Hkeff may be attributed to an increase and decrease in Ku, respectively. The increase in Hc(perp) caused by the addition of carbon is probably due to the increase in Ku and/or to the refinement of the magnetic domain. The decrease in Hc(perp) may be attributed to the decrease in Ku even though the magnetic domain is refined.