The dissertation thesis deals with the influence of the temperature of saturated water steam and time on the targeted modification of the colour of deciduous wood: Fagus sylvatica, Betula pendula, Acer pseudoplatanus, Alnus glutinosa in three modes of modification and four time periods. From analysis of theoretical basis it is known that during the process of wood colour modification with saturated steam in a pressure autoclave there are changes in the properties of modified wood in terms of physicochemical properties (colour, moisture, density and acidity of wood), which are examined and evaluated in the present dissertation work. The second part of the dissertation thesis consists of field tests and experimental measurements of physical and chemical properties of modified wood in operating and laboratory conditions. During the process of colour modification, a targeted change of colour was achieved, resp. colour shade of wood in individual modes and times, where the wood reached more or less significant colour shades of yellow, red, pink and brown, as well as their mutual combinations depending on the temperature of saturated water steam and the time of modification. We can say that with the higher temperature of saturated water steam and the longer the time of its action on the wood in the pressure autoclave, the more uniform and richer change of colour or colour shade was achieved. The achieved change in the colour of the wood had a full-volume character, which had been proven both by measurements of the colour of the wood and by visual inspection on the sawn surfaces of the blanks. The dissertation thesis contains a range of achieved changes in the colour of modified wood in individual modes and times of modification for visual evaluation of the effectiveness of the technological process. The final evaluation of the measured data shows that the wood moisture does not change during the modification process, but during the cooling to ambient temperature due to the evaporation of water from warm wood, the wood moisture decreases. The density of modified beech, birch, maple and alder wood shows a slight decrease. The acidity of wet wood decreases, while the rate of increase in acidity is significantly influenced by the temperature of saturated water steam and the time of modification. One of the last aim of the work was to determine the effect of daylight on the change of colour of the wood surface. Based on the evaluation of the 24 months of samples exposure of native and modified wood species, it can be stated that the surface of native samples darkens and the surface of modified wood fades.