A laser particle size analyzer was used to analyze the particle size composition of -200 mesh from the coals for different grinding time and/or different microwave pre-treatment time. Fourier-transform infrared was used to show the changes in the main functional chemical groups of oxidized coal upon grinding and/or microwave pre-treatment. All of these were recognized by the flotation behavior using an XFD1.5L flotation cell. Under the same grinding time, -200 mesh coals will be finer when microwave pre-treatment increases. Microwave pre-treatment and grinding improve the floatability of oxidized coal by reducing the content of –OH and/or increasing the content of –CH3. Combustible recovery increases or decreases proportionately with a yield of -74 C11 m.