A new mechanistic methodology of scale-up for gas-solid spouted beds has been proposed and validated which is based on maintaining similar radial profiles of gas holdup. Two spouted beds of 0.152 m and 0.076 m inside diameter have been used. The local measurements of the dimensionless solids velocity and holdups using an advanced optical fiber probe and pressure fluctuations using pressure transducers indicate clearly the similarity when the radial profiles of the gas holdups were kept similar in the two studied spouted beds. When the radial profiles of the gas holdups were different in the two studied spouted beds, the dimensionless of the local studied parameters mentioned above were different. The differences increase when the difference in the magnitudes and trends of the gas holdup profiles increases.