Abstract: Testing samples were collected from the heartwood of healthy oak trees in Eastern Serbia. Over the periods of two, four and six months, the wood samples were exposed to the mycelia of the fungus that causes cubical brown rot on oak - Laetiporus sulphureus (Bull. ex Fr.) Murrill (Sulphur Polypore).The contribution of Laetiporus sulphureus (Bull. ex Fr.) Murrill to the decrease in the bending strength of Q. petraea wood was investigated. After two, four and six months of being under the effect of L. sulphureus, the static bending strength of oak wood substantially decreased compared to the initial value (100%) and amounted to 91.73, 75.17 and 63.25%. The regression line obtained through data processing opened up the possibility to predict the changes of wood properties in certain time periods of the fungus effect under the unchanged environmental conditions.
       Keywords: bending strength, sessile oak