Romarheimsfjorden is a fjord in Hordaland county, Norway. The fjord flows through the municipalities of Modalen, Lindås, and Osterøy. The western end of the fjord lies near the island of Hokøy where the fjord flows in to the Osterfjorden on its way out to sea. The fjord extends eastward from Hokøy for along the border of Lindås and Osterøy before entering Modalen where it continues to the Mostraumen, a wide channel that is long. On the other side of the channel, the fjord continues for another where it is usually called the Mofjorden. That fjord ends at the village of Mo.