The suppression of spread of flame over A-Heavy oil pool by W/O (water-in-oil) type emulsification was studied experimentally in detail. W/O emulsified A-Heavy oil, in which the water content is 2-10 vol %, was prepared by mixing A-Heavy oil with water without surface active agent in the gear pump type emulsification apparatus. The effects of W/O emulsification on the flash point, the velocity of flame spread over the pool and on the development of preceding surface flow ahead of flame leading edge were studied. The results were discussed comparing the W/O type emulsified A-Heavy oil with the original one, The flash point of the W/O emulsion rises 2 ∼ 4°C from that of the original A-Heavy oil with increase in the water content up to 2 vol %. The velocity of flame spread can be suppressed owing to the emulsification to about ½ ˜ ⅔of that over the original A-Heavy oil. Preceding surface flow ahead of flame is promoted owing to the emulsification. From these results, the present study concludes that the suppression of flame spread by the emulsification is mainly due to both the rise in flash point and the increase in convective heat loss caused by elongated surface flow.