Mayor Laura Prati was reported in serious condition at a nearby hospital after being shot in her office by a man with a pistol, the Italian news agency ANSA reported.
The town's deputy mayor was also injured in the incident.
Police identified the gunman as Giuseppe Pecoraro, a former municipal policeman who had recently been transferred to an administrative position.
"I have settled the scores," Pecoraro reportedly said after the shooting.
Cardano al Campo is near Milan.
Ohio bar shooting arrested, charged with murder
Beautician charged with giving client fatal silicone butt injection