Low-ash anthracite coal particles with 0.5-0.25 mm size fraction were used to investigate the effect of shape properties on the natural floatability of coal. The flotation tests were conducted using flotation rate in order to obtain several types of froth products in the absence of collectors. Froth products were forwarded to the particle shape measurements using microscope technology associated with image analysis by MATLAB software. The roundness of coal particle was introduced to indicate the shape property. Throughout this paper, it was found that the coal particle with lower roundness floated quickly, while the coal particle with higher roundness floated slowly. The ash content of quickly floated particle is similar to that of slowly floated coal particle. It then can be concluded that the natural floatability of low-ash coal particle is primarily determined by the shape of coal particle.