Carbon was introduced by arc melting to RTiFe11, where R=Sm, Gd, Th, Dy, Ho, Er, and Y, and its effects on the crystallographic and magnetic properties of these compounds have been investigated by x‐ray and magnetic measurements. The experimental results show that the carbon atoms occupy 8isites in ThMn12structure. It is found that the substitution does not have an effect on the Curie temperature, but instead increases both saturation magnetization and magnetocrystalline anisotropy. The intrinsic magnetic properties of SmTiFe11are improved with the addition of the carbon atoms, indicating that SmTiFe11−xCxis a better candidate for permanent magnetic applications than SmTiFe11.