In this study, compressive behavior of form-block-wall was studied through prism test. In the experiment, main variables are the difference in mix design of block and strength of grout concrete. Experiment result showed that the prism strength of form-block-wall increased in proportion to the strength of grout and block. The initial stiffness in load-displacement curve varied corresponding to the difference of block strength in low strength of grout concrete while there was not a difference of it in the case of high strength of grout concrete.