To examine the forest structure and variation of samara and leaf shape of Acer pictum subsp. mono (APSM), We investigated forest structure and samara angles and length, and leaf shape in three natural population of APSM in Yanggu-gun, Youngyang-gun and Kwangyang-si from June 2012 to October 2013. Mean importance percentage (MIP) of APSM is shown lower values in Yanggu 19.8%, in Youngyang 22.0%, and in Kwangyang 17.1%, respectively. In middle layer, importance percentage (IP) of APSM is shown lower values than that of Acer pseudosieboldianum and Carpinus cordata. In lower layer, importance percentage (IP) of APSM is shown lower values in Yanggu 1.8%, in Youngyang 1.9%, and in Kwangyang 0.0%, respectively. From these results, MIP of APSM in natural population might be reduced in future. Angles between wings and samara length are significantly different between districts. APSM with seven palmate vein leaf are distributed more frequently at Kwangyang and Youngyang than Yanggu. Percentages of biserrate leaf is shown in Yanggu 0.6%, in Youngyang 15.8%, and in Kwangyang 20.4%, respectively. These results implies genetic variation in natural APSM population and further studies on the genetic variation analysis in natuel population of APSM should be needed.