Diamond-like carbon (DLC) is an attractive biomedical material due to its high inertness and excellent mechanical properties. Using plasma immersion ion implantation-deposition (PIII-D), DLC films are fabricated on silicon substrates at room temperature. By changing the C2H2 to Ar(FC2/H2/FAr) flow ratio during deposition, the effects of the reactive gas pressure and flow ratio on the characteristics of the DLC films are systematically examined to correlate to the blood compatibility. The thickness, surface morphology, composition, structure, sp3/sp2 content, as well as carbon–hydrogen bonding are studied using alpha-step profilometry, atomic force microscopy (AFM), Rutherford backscattering spectrometry (RBS), Raman spectroscopy, and Fourier transform infrared spectroscopy (FTIR), respectively. The blood compatibility of the film is evaluated using in vitro platelet adhesion investigation, and the quantity and morphology of the adherent platelets are investigated employing optical microscopy and scanning electron microscopy (SEM). The Raman D-band to G-band intensity ratio is consistent with the adherent platelet quantity. Both first increase and then decrease with higher FC2/H2/FAr flow ratios. This implies that the blood compatibility of the DLC films is influenced by the ratio of sp3 to sp2, not by the absolute sp3 or sp2 content. Our study suggests that DLC films with the proper sp3 to sp2 ratio and good blood compatibility can be fabricated by C2H2-Ar PIII-D using a suitable C H yAr gas ratio.