Abstract: The invention provides a grease trap and a method of decomposing edible oils and fats using the grease trap. The grease trap for storing the drainage includes a drain inlet for introducing drainage from a kitchen through a drainpipe and a drain exit for discharging the drainage to a sewer, and accommodates an impeller unit having an impeller which continuously rotates to stir and splash the drainage surface, or a sprinkler unit which continuously sprinkles the drainage onto the drainage surface. The decomposing method comprises the steps of storing the drainage from a kitchen in the grease trap, supplying aerobic microorganisms into the drainage, and continuously stirring and splashing the surface of the drainage using the impeller unit or continuously sprinkling the drainage onto the drainage surface using the sprinkler unit, thereby activating the aerobic microorganisms.