Si- and N-doped diamond-like carbon (DLC) coatings with various Si and N contents were deposited on glass slides using magnetron sputter ion-plating and plasma-enhanced chemical vapour deposition. Surface energy analysis of the DLC coatings revealed that with increasing Si content, the electron acceptor value decreased while the electron donor value increased. The antifouling property of DLC coatings was evaluated with the bacterium, Pseudomonas fluorescens, which is one of the most common microorganisms forming biofilms on the surface of heat exchangers in cooling water systems. P. fluorescens had a high value of the component (69.78 mN m −1 ) and a low value of the component (5.97 mN m −1 ), and would be negatively charged with the zeta potential of −16.1 mV. The experimental results showed that bacterial removal by a standardised washing procedure increased significantly with increasing electron donor values and with decreasing electron acceptor values of DLC coatings. The incorporation of 2%N into the Si-doped DLC coatings further significantly reduced bacterial attachment and significantly increased ease of removal. The best Si-N-doped DLC coatings reduced bacterial attachment by 58% and increased removal by 41%, compared with a silicone coating, Silastic® T2. Bacterial adhesion strength on the DLC coatings is explained in terms of thermodynamic work of adhesion.