Co thin films were deposited by remote plasma atomic layer deposition (ALD) method using dicobalt hexacarbonyl t-butylacetylene (C12H10O6(Co)2) or cyclopentadienyl cobalt dicarbonyl (CpCo(CO)2) as the Co precursor. The impurity contents were minimized when the Co films deposited by remote plasma ALD with H2 plasma within the process pressure range of 0.1~2 Torr at plasma power of 300W. Co-Cp bond in CpCo(CO)2 precursor was easily broken under H2 remote plasma atmosphere. The carbon content of Co films were examined with Auger electron spectroscopy (AES) and Rutherford backscattering spectroscopy (RBS) to be ~21 at.% with C12H10O6(Co)2, and ~7 at.% with CpCo(CO)2. The surface morphologies of Co films were measured with atomic force microscope (AFM) and root mean square (RMS) values of Co films using C12H10O6(Co)2 and CpCo(CO)2 were 1.73 and 1.51, respectively.