A worker thought a colleague was playing a joke on her when the corn snake turned up at Clyde Defence Lawyers on Alexander Street in Clydebank, near Glasgow.
The Scottish SPCA rescued the orange and yellow reptile, which has been named Tango, and took it into the charity's animal rescue and rehoming centre in Cardonald, Glasgow.
SSPCA animal rescue officer Emma Campbell said: "The person who first spotted Tango didn't think he was real as he wasn't moving.
"She thought someone in the office was playing a prank on her but after a colleague gave him a gentle prod it was clear he wasn't a toy and that they needed to contact us for help.
"Tango is a placid wee guy and he isn't very big as he's still a juvenile."
Ms Campbell appealed for Tango's owner to come forward after his discovery on Thursday. She said: "We'd love to reunite Tango with his owner if he has gone missing but if no-one comes forward, we'll find him a new home."