This paper presents the stress-strain behavior of structural synthetic fiber-reinforced cellular lightweight concrete (CLC) stack-bonded prisms under axial compression. Masonry compressive strength is typically obtained by testing stack-bonded prisms under compression normal to its bed joint. CLC prisms with cross-sectional dimensions of 200 x 150 mm (7.87 x 5.90 in.) with an overall height of 470 mm (1.54 ft) were cast with and without different dosages of synthetic fiber reinforcement. Polyolefin was used as a structural fiber reinforcement at different volume fractions (vf) of 0.22, 0.33, 0.44, and 0.55% with and without microfiber dosage of 0.02%. Experimental results indicate that the presence of fibers helps in the improvement of strength, stiffness, and ductility of CLC stack-bonded prisms under compression. Test results also signify that the hybrid fiber reinforcement provides better crack bridging mechanism both at micro and macro levels when compared to only macrofibers. Simple analytical models were developed for stress-strain behavior of CLC blocks and stack-bonded CLC prisms based on the experimental results with and without fibers under compression. © 2018, American Concrete Institute. All Rights Reserved.