This study compared the number of individuals Musca domestica and Megaselia scalaris caught in multiple vertically placed traps to determine the effective placement of height of traps for monitoring. The number of M. domestica decreased significantly as the height of the light trap increased. The number of M. scalaris was largest in the highest trap when 2 or 3 traps were operated. There was no significant difference in the number of M. domestica and M. scalaris caught at different heights when only one light was turned on, which suggested that both species were attracted to the light at any height, regardless of their height preferences. These results indicate that when multiple traps are used for indoor monitoring of flies, the traps should be set at a uniform height.