A novel approach has been proposed to enhance the flame retardancy of polypropylene (PP) by a flexible and highly efficient intumescent flame-retardant coating, avoiding the damage to intrinsic properties of PP caused by high loading of flame retardant additives. The flame-retarded PP specimen with a coating in an average thickness of 126 lm passed V0 rating at UL-94 test, whose limiting oxygen index (LOI) value reached up to 30.5 vol%. Its heat release rate (347 kW/m(2)) was reduced by 71.2% comparing to pure PP, showing a satisfactory flame retardancy. More importantly, the smooth coating was flexible to deform with the substrate and could not fall off, due to strong adhesion and great mechanical properties. The mechanisms of flame retardancy and strong adhesion of the coating were fully demonstrated. In addition, the coating is anti-ultraviolet and water resistant. This approach will be promising for the development of intumescent flame-retardant coatings for plastics. (C) 2017 Elsevier B.V. All rights reserved.