Fan Gyhirych is a mountain in the Fforest Fawr section of Brecon Beacons National Park in south Wales.

The hill drains to the north into the catchment of the Afon Crai and to the south and west into that of the River Tawe.

The Cribarth Disturbance, a north-east to south-west aligned zone of faulting and folding, passes through the hill.

The hill's finest feature is its north-eastern cwm which held a small glacier during the ice ages.

[3] Along the lower western flanks of the hill, entrepreneur John Christie ran the Brecon Forest Tramroad in the early part of the nineteenth century.