It was found that atomically flat Co(110) film could be grown on Cu(110) using O as a surfactant. To obtain detailed knowledge on the effect of O on the growth, as well as on the magnetic properties of Co overlayer, we carried out an investigation on this system using Auger Electron Spectroscopy (AES), Low Energy Electron Diffraction (LEED), Surface Magneto-Optic Kerr Effect (SMOKE), and Scanning Tunneling Microscopy (STM). With O as a surfactant, the initial growth of Co (<1 ML) results in a flat monolayer structure. When the Co is thicker than 1 ML, three-dimensional clusters begin to form. These clusters become ordered islands at 3 ML Co and coalesce at ~5 ML Co. Above 5 ML Co, layer-by-layer growth resumes. No Cu segregation is observed. SMOKE studies at room temperature show that the Co film is magnetic above ~5 ML Co, with the magnetization easy axis along the  direction. On the other hand, without using oxygen as a surfactant, Co grows three-dimensionally on Cu(110). The Co overlayer has its easy magnetization axis along the  direction, but the onset of the magnetization was observed at 11 ML Co at room temperature.