The colonization of tiny marine organisms on ship's hull which are connected directly from seawater, is a costly issue. Biofouling contributes to enhanced hydrodynamic drag, which leads to higher consumption of fuel and greenhouse gas emissions. Therefore, the environment-friendly solution is very necessary for anti-biofouling activity. For this purpose, we have synthesized biodegradable polyurethane (CL-PU) composed of ε-CL and 4,4′-methylenebis(cyclohexyl isocyanate) (H12MDI) and 1,4 butanediol (1,4 BD). The synthesized CL-PU was further modified with 4, 5-dicholoro-2-octyl-isothiazolone (DCOIT) and clay by mixing of the solution to make composites. Our study showed that CL-PU/DCOIT/clay composite degraded in the artificial seawater (ASW), enzymatic solution and seawater (through laboratory test) due to the contents of clay. Because the existence of clay reduced the size of the spherulite of polycaprolactone (PCL) in the composite, therefore remarkably improved the crystallinity as determined via the polarizing optical microscope (POM) and differential scanning calorimetry (DSC). The composite acted as carrier of antifoulant (DCOIT) and controlled their release rate. The anti-bacterial and anti-diatom experiments exhibited that the composite with DCOIT contents were effective in preventing the accretion of Escherichia coli (E.coli) (region inhibition 14 mm) and marine diatom Navicula incerta (82.5% reduction). The degradable CL-PU/DCOIT/clay composite will have tremendous durability and excellent anti-fouling activity for marine biofouling owning to sustainability and tunability without being toxic to aquatic biota. Display omitted •Biodegradable composite synthesized by mixing of the solution method.•The clay reduced the crystallinity and spherulite size of the PCL in the composite.•The environmentally-friendly composite prevents the early stage of biofouling.