The fire broke out before 10:00 a.m. Tuesday at the Red Clay Creek Apartments in the 2100 block of Grafton Drive in Mill Creek.
Crews arrived to find fire and heavy smoke pouring from the two-story, garden-style apartment building.
A second alarm was struck at 10:14 a.m. before firefighters were able to get the upper hand.
No injuries were reported. However, the flames caused $200,000 in damage.
Five people have been put out of their homes.
Officials say this is the second arson at the complex in less than one month.