The fires were reported at Evergreen Valley High School at 830 N. Capitol Ave. at 2:36 a.m., Capt. Reginald Williams said.
One of the fires was in a dumpster, while the other was set by the wall of the school's library, Williams said.
A second alarm response was called, and the fires were under control a little over an hour later.
The exterior of the building sustained moderate damage, Williams said.
A fire investigator was called to the scene and firefighters are treating the two fires as suspicious.
No one was injured. There were no classes scheduled in the school for today because students are on summer break, Williams said.
