An experimental study was made to explore the air entrainment into heptane pool fires and the smoke blocking effect on thermal radiation from fire. Heptane was burned in five different sixed tanks 0.3 m, 1 m, 2 m, and 6 m in diameter, and its burning rate, flame temperature,vertical hot gas velicity, and thermal radiation were measured. It was found that the total amount of air entrainment is about 5 times the stoichiometric air requirement. A smoke block effect appeared at tank diameter of 2 m or more.