Intumescent coating is an insulating system designed to decrease heat transfer from a fire to substrate structure to maintain its integrity. Zinc phosphate was used as primer coating on steel coupons for better protection from corrosion. The coating was based on Expandable graphite (EG), ammonium poly phosphate (APP), melamine, boric acid (B.A), bisphenol A epoxy resin BE-188 (BPA) and ACR Hardener H-2310 polyamide amine. Different formulations were developed to study the bonding of coating with steel substrate. The Intumescent coating was tested at 500°C for one h and it was found very stable and well bound with the steel substrate. Scanning Electron Microscope was used to study microstructure the substrate and bonding mechanism of coating with substrate after fire test. The results confirmed that coating was well bounded with steel substrate after fire test. © 2011 Asian Network for Scientific Information.