Fly ash class F from Thermal Power Plant “Stanari” was used in combination with highly plastic brick clay from Busovača to develop building bricks. The brick clay and fly ash were characterized for chemical and mineralogical composition, grain size distribution, and specific gravity. The fly ash has a higher proportion of larger particles and lower specific gravity than clay. The brick clay was mixed with 20, 40, and 60 wt. % of fly ash, formed in a prismatic shape, dried and then fired at 800, 900, and 1000 °C. The fired prisms were characterized for water absorption, apparent porosity, apparent density, and strength and compared with conventional clay prisms. The addition of fly ash of 20, 40, and 60% reduced the mass of the samples by 14, 23, and 31%, increased apparent porosity by 60, 100, and 160%, and reduced the compressive strength by 50, 80, and 90%, respectively. Conducted tests and comparative studies have shown that the fly ash “Stanari” can be used as an additive to the clay “Čavka” in the maximum amount of 20 % and the optimum firing temperature is 900 °C.