Police were called to reports of a fire at the Goat Ledge Café on Lower Promenade, Warrior Square, St Leonards, shortly after 11pm on Saturday (February 27).
The fire was extinguished by crews from East Sussex Fire and Rescue Service.
On Monday (March 1), a spokesman for Sussex Police said the cause of the fire was found to be deliberate, and police enquiries are now ongoing.
The spokesman added: “Anyone who saw what happened, witnessed any suspicious behaviour in the area around that time or who may have any relevant CCTV or dash cam footage is asked to contact police online or by calling 101 quoting serial 1604 of 27/02.”
East Sussex Fire and Rescue said crews were called 11.03pm on Saturday to reports of ‘smoke coming from a café on Grand Parade, St Leonards’.
Three fire engines attended and used two breathing apparatus and a hose reel jet to extinguish the fire.
A spokesman said the incident was left with the police.