Most of the wood preservatives represent a potential danger for environment and human beings, while wood protecting, treating, using, and decaying. Therefore, lately, there is a tendency to develop a new environment friendly procedures to protect it. One of the possibilities is a modification. The specimens, modified with various silicon compounds, prepared at the Institute of Wood Biology and Technology in Göttingen (Germany), were tested then at faculty, in accordance with the SIST EN 152/2 standard instructions, and exposed to the suspension of blue stain spores Aureobasidium pullulans and Sclerophoma pithyophilla. It was found out that the modification with silicon compounds did not protect wood against blue stain fungi, with the exception of Siliconat 1, which prevented wood colouring.