ABERSYCHAN, an urban district in the northern parliamentary division of Monmouthshire, England, 11 m. N. by W. of Newport, on the Great Western, London and North-Western, and Rhymney railways. Pop. (1901) 17,768. It lies in the narrow upper valley of the Afon Lwyd on the eastern edge of the great coal and iron mining district of Glamorganshire and Monmouthshire, and its large industrial population is occupied in the mines and ironworks. The neighbourhood is wild and mountainous.