Officers were called out to the John W. Wells Youth Center Tuesday night on 5th and Flume Streets.
About a quarter of the structure was destroyed by the flames.
City officials say this is the second incident of a playground fire in Madera this week, following a fire at the Rotary Park playground last Sunday.
Investigators also found evidence that accelerants may have been used in both cases.
There's no word of any arrests in either incident.