Four crews are trying to bring a fire under control on Holyhead Mountain.
Up to sixty firefighters were at the scene of the blaze on Mynydd Tŵr, which broke out at around 7.30pm on Sunday evening.
Crews from Llangefni, Rhosneigr, Amlwch and Holyhead are still on site, but the fire has died down considerably.
Around 5,000 sq m of grassland have been affected but North Wales Fire and Rescue Service say there is no risk to nearby homes.
Elsewhere on Anglesey, grass fires have also been reported at South Stack and Plas Meilw near Holyhead.