The research was performed in the plantation or euramerican poplar clone I-214 with spacing 5 × 5 m, i.e. 400 trees per ha, on habitat of the first site class in Lower Danube Basin. In the 13 year old plantation, on three experimental plots, each with area of 0.12 ha, the thinning was performed, by which the number of trees was reduced to achieve density of 200 trees·ha-1. Experimental plots are part of the design of broader experiment in which the research on production and space regulation for tree growth in different plantation ages is performed. Predominantly, by thinning, the competitors to the trees with favourable characteristics and the trees that stagnated in growth were removed. Thus, according to the fact that number of trees was reduced by 45%, the total basal area by 33% and volume by 32%, the thinning could be considered as heavy, and low by character (qd= 0.79). As the thinning was performed in 13 years after the plantation establishment, i.e. five years after the ending of intensive height growth, it could be considered to be late. Trees that remained after the thinning had two-times smaller variability of diameter (cv), i.e. the plantation is homogenised for the production of the most valuable assortments until the end of the rotation. Achieved allowable cut was 109 m3·ha-1 in average, 90 m3·ha-1 of which was in the category of technical assortments, worth 3.090 €·ha-1 in total. The costs of cutting, creating and transporting of the assortments, as well as the difference between establishment costs for plantation with 400 trees·ha-1 and plantation with 200 trees·ha-1, are 1.325 €·ha-1, which is less than a half of the worth of the assortments gained by thinning (3.090 €·ha-1) and shows high economic profitability of such operation.