Alder wood (Alnus glutinosa L.) was steamed with a saturated steam-air mixture at a temperature of t = 95 °C, or saturated steam at t = 115 °C and t = 135 °C to obtain a pale brown colour, a light red-brown colour and a dark brown-grey colour. Subsequently, samples of unsteamed and steamed alder wood were irradiated with a UV lamp in a Xenotest Q-SUN Xe-3-HS after drying in order to test the colour stability of steamed alder wood. The colour change of the wood surface was evaluated by means of measured values on the coordinates of the colour space CIE L*a*b*. The results show that the surface of unsteamed alder wood as well as steamed alder wood with a steam-air mixture at t = 95 °C and saturated steam at t = 115 °C darkened and browned due to photochemical reactions caused by UV radiation. The opposite tendency was recorded at the surface of alder wood steamed with saturated steam with a temperature of t = 135 °C, where the deep dark-brown-grey colour lightened to a brown-reddish colour shade under the influence of UV radiation. The analysis of the changes in the coordinates of the colour space CIE L*a*b* shows that the greater the darkening and browning of the alder wood by steaming, the smaller the changes in the values of ΔL*, Δa*, Δb* of the steamed alder wood caused by UV radiation. The positive effect of steaming on UV resistance is evidenced by the decrease in the overall colour difference ΔE*. While the value of the total colour difference of unsteamed alder wood caused by UV radiation is ΔE* = 10.9, it decreased to ΔE* = 8.7 for alder wood steamed with steam-air mixture at t = 95 °C, which is a decrease of 20.2 %; for alder wood steamed at t = 115 °C it decreased to ΔE* = 6.5, which is a decrease of 40.3 %; and for alder wood steamed with saturated water steam with the temperature t = 135 °C it decreased to ΔE* = 5.7, which is a decrease of 47.7 %. Za potrebe ispitivanja drvo johe (Alnus glutinosa L.) pareno je smjesom zasićene pare i zraka na 95 °C odnosno zasićenom parom na 115 i 135 °C kako bi se dobila blijedosmeđa, svijetla crvenosmeđa i tamna smeđosiva boja. Nepareni i pareni uzorci drva johe nakon sušenja su ozračeni UV lampom u uređaju Xenotest Q-SUN Xe-3-HS kako bi se ispitala stabilnost boje parenog drva. Promjena boje površine drva procijenjena je uz pomoć vrijednosti izmjerenih u koordinatnom sustavu boja CIE L*a*b*. Rezultati su pokazali da je površina neparenog drva johe i drva johe parenog smjesom pare i zraka na 95 °C te drva parenog zasićenom parom na 115 °C zbog fotokemijskih reakcija uzrokovanih UV zračenjem potamnjela i posmeđila. Suprotna je promjena zabilježena na površini drva johe parenoga zasićenom parom na 135 °C, na kojemu je tamna smeđosiva boja pod utjecajem UV zračenja posvijetlila i poprimila smeđocrvenkasti ton. Analiza promjena u koordinatnom sustavu boja CIE L*a*b* pokazuje da UV zračenje uzrokuje niže vrijednosti ΔL*, Δa*, Δb* parenog drva johe što je tamnjenje i smeđenje drva johe zbog parenja jače. Pozitivan učinak parenja na otpornost prema UV zračenju vidljiv je po smanjenju ukupne promjene boje E*. Tako je vrijednost ukupne promjene boje neparenog drva johe nakon UV zračenja parenjem smjesom pare i zraka na 95 °C smanjena s E* = 10,9 na E* = 8,7 (smanjenje od 20,2 %), parenjem zasićenom parom na 115 °C smanjena je na E* = 6,5 (smanjenje od 40,3 %), a parenjem zasićenom parom na 135 °C zabilježeno je smanjenje od E* = 5,7 (smanjenje je iznosilo 47,7 %).