This study was carried out to estimate the aboveground-biomass of Machilus thunbergii, warm-temperature evergreen broad leaved tree, growing in the seashore near Bogil island located at the southern part of the Korean peninsula. The bark of M. thunbergii was used for medicine in the Korea. The results were summarized as follows : 1) The aboveground-biomass was 123.708 tons/㏊ and the biomass of branch bark greater than 3㎝ in branch diameter was 1/5 of total bark mass(8.095 tons/㏊). Dry matter density was 1.77 ㏊/㎥ and leaf area index 8.08. 2) Net production of the stand was estimated as 16.051 tons/㏊/yr and the leaf was the greatest, followed by stemwood, branchwood, stem-bark and branch-bark. 3) The net assimilation rate of the stand was 1.384 ㎏/㏊/yr. The efficiency of leaves to produce stem was 0.451 ㏊/㏊/yr and that of bark 0.051 ㏊/㎏/yr. Biomass accumulation ratio was 7.707㏊/㏊/yr.