Alcosser (Valencian: [alkoˈseɾ] or Alcocer de Planes Spanish: [alkoˈθeɾ ðe ˈplanes]) is a municipality in the Valencian comarca of Comtat, in the province of Alicante, Spain.

It is situated on the shore of the Serpis river, south of the Serra de Benicadell, in the central part of the Foia de Cocentaina. It is bordered on the north by Gaianes, on the east by Planes, on the west by Muro d'Alcoi, and on the south by Benimarfull.