The changes in microclimatic conditions after thinning was analysed in a young spruce forest at an ecological experimental study site at Bílý Kříž (the Moravian-Silesian Beskids, the Czech Republic) during the growing season 2001. The microclimatic profile measurements were carried out in and above the forest at two plots with different stand density. The first plot Fd had the stand density of 2600 trees/ha, while at the adjacent plot Fs the stand density was reduced after thinning to 1800 trees/ha. The vertical profiles of air temperature, relative humidity, and wind speed on the plots Fd and Fs were evaluated in the period June-October 2001. The results of the analysis showed that thinning has as a result the decreasing in the relative humidity above the forest. Since the air temperature at the plot Fs with thin forest was generally very similar to the corresponding value in the dense forest Fd, it can be concluded that the thinning significantly increased the evaporative demands of air above the canopy. Further, an expected increasing of wind speed in the forest after its thinning was recorded. Nevertheless, some wind speed reduction was simultaneously observed above the canopy of the thinned forest what can be explained as a result of difference in the roughness length which was greater at Fs plot than at Fd plot during the whole growing season 2001. Consequently, this wind speed reduction can be considered as an effect of stronger breaking of the air flow above the canopy at Fs plot in comparison with the situation at the plot Fd.