We studied the incomplete 3d-transition metal-lements, scandium through nikel, atoms and their corresponding cations by diffusion Monte Carlo (DMC) method with three different basis sets, namely VTZ ANO, Stuttgart RSC 1997 ECP, and CRENBL ECP. Our calculations for total ground state energy and first ionization potential, agree very well with studies used LANL2DZ B3LYP as basis sets, and with the experimental values of first ionization potential. Moreover, we found that the calculations with VTZ ANO basis set are more accurate than those with the other two basis sets.