A skip was set ablaze in a car park at Cardinal Newman College in Preston.
Firefighters were called to Lark Hill Road at around 1.50pm on Saturday.
They said the rubbish inside was well alight when they arrived at the scene and the incident lasted around 45 minutes.
It is believed the fire was started deliberately.
Firefighters asked anybody who witnessed the fire or anybody with any information about the blaze to call Lancashire Police on 101.