An engine starter mounting structure is provided that basically has a starter housing part, a starter insertion part, a first flange part and a second flange part. The starter housing part has an internal portion that at least partially houses a portion of a starter. The starter insertion part is arranged to provide access to the internal portion of the starter housing part for inserting the portion of the starter into the internal portion. The first flange part is disposed on an end portion of the starter housing part with the first flange part including a fastening structure that is configured to fasten the starter thereto. The second flange part is disposed in the internal portion of the starter housing part, with the second flange part having a bolt hole that is arranged and configured to receive a bolt therethrough for interconnecting an engine and a transmission together.