Swelling characteristics of three kinds of single coal particles heated with a well-characterized CO2 laser were directly observed and quantitatively evaluated by combined application of a highspeed video camera with an image analysis system, The results areas follows : (1) The interval time between swelling and shrinking of bubbles of coking coal particles (Blue Creek, Goonyella) could be used to express the ease of reforming bubbles after bursting and the growth of the bubbles before bursting, The distribution of the interval time of coking coals depends on laser intensity, particle size, and coal properties. (2) For the high-volatile weak coking coal (Witbank), there is no formation of bubbles during heating and the maximum swelling ratio is much smaller than that of coking coals. (3) The maximum swelling ratio and final swelling ratio evaluated with the relative projection area decrease with the increasing of laser intensity (or temperature and heating rate) and particle size. (4) There is a monotonously increasing relationship between the maximum relative projection area and the maximum Gieseler fluidity for all three kinds of coal, although the maximum relative projection area increases with increasing laser intensity. This result suggests that the relative projection area of coal particles on heating can be used for evaluating both the swelling and fluidity properties of coals, (5) The present results suggest a possibility that the "surface tension" of bubble film of the coking coal on heating seems to be attainable from the calculation of the rupture pressure of bubbles.