We have developed a convenient and modern method for obtaining amidoximes from aryl‐ or heteroaryl nitriles and hydroxylamine hydrochloride in the presence of a base using mechanochemical activation of the starting compounds. The method does not require the use of large volumes of solvents; the reaction occurs at room temperature for 2 h and provides high isolated yields of the corresponding amidoximes for most of the nitriles studied. We were also the first to use a mechanochemical approach to modify polysiloxanes. We demonstrated the possibility of synthesizing a functionalized copolysiloxane containing amidoxime functions and showed that the use of mechanochemical activation allows one to overcome one of the fundamental difficulties encountered by synthetics in the functionalization of polysiloxanes—reaction heterogeneity.