High phosphorus electroless nickel bath has been used to prepare composite coatings containing SiC particles (40 nm, 3 mm and 7 mm). The coated samples were subjected to heat treatment at 400 °C for 1h. The effect of heat treatment on the microstructure of Ni-P-SiC composite coatings was investigated by X-ray diffraction. Potentiodynamic polarization measurements made on these deposits in 3% sodium chloride solution showed that corrosion resistance in nano-composite coatings was much higher than micro-composite coatings. The corrosion rate results for nano-composite coatings showed a 6 fold improvement as compared to the micro-composite coatings.