Mechanoactivation effect has been studied on crystal structure of BaAl2Si2O8 known as polymorphous compound. Ultrasonic treatment of the synthesized material powder has been used as mechanoactivation method. Ultrasonic grinding during 0.5–1.5 h was determined to result in polymorphous transformation. Dielectric properties of ceramics BaAl2Si2O8 have been investigated for hexagonal, monoclinic modifications of crystal structure as well for that based on phase mixture. It is shown that sintering of ceramic material based on monoclinic crystal structure modification of BaAl2Si2O8 takes place in temperature diapason of 1300– 1350ºС. Ceramic materials based on BaAl2Si2O8 compounds have been shown to exhibit low porosity, high Q-factor and dielectric parameters allowing use them for resonators, and other microwave devices