Particle size effects on boiling performances of micro-porous enhanced surfaces are studied using five different sizes of diamond particles. By comparing the coating thicknesses with the superheated liquid layer thickness, the coatings are classified into two groups : ’micro-porous’ and ’porous’ coatings. The superheated liquid layer thickness is calculated using one-dimensional transient thermal conduction. Micro-porous coating shows different characteristics of boiling performances compared to porous coating in incipient superheat, nucleate boiling and CHF.