Abstract: This study presents a method for estimating the strength of lightweight aggregate. Cylindrical specimens with various aggregate volume ratios (volume of coarse aggregate/total aggregate volume) were cast and tested. Micromechanics method was applied by considering a perfect bond between mortar and aggregate. The approximate aggregate strengths determined from the concrete strength, component properties, and the volume ratio of aggregate are between 15 and 30 MPa. Both matrix strength and composite strength are much higher than the lightweight aggregate strength.