This paper presents a case study for strengthening a post-tensioned slab using carbon fiber reinforced polymer (CFRP). Major steps that need to complete a strengthening process are analysis of a structure and then design for strengthening a structure with CFRP. However, a pull-off test for an epoxy resin by following ASTM D4541 and a load-carrying capacity test is an option that can be done to prove and make sure that the material used is acceptable and strengthened structure can resist new load conditions. For safety concerns, an existing strength of the structure should be sufficient to resist a level of this factored load (1.1DL + 0.75LL). If the CFRP system is damaged, the structure will still be capable of resisting a reasonable level of load without collapse. In this case study, the unstrengthen capacity of the slab without CFRP is 8,609 kg-m/m. The new design load with the factor from the analysis is 9,670 kg-m/m, and slab after strengthening with CFRP can resist bending moment at 11,483 kg-m/m while the slab displacement measured from the load test is acceptable compared with its span.