The principal objective of this paper is the investigation of experimental and theoretical flexural behavior of reinforced high strength concrete one-way slabs strengthened or repaired with externally bonded carbon fiber reinforced polymer (CFRP) sheets. The experimental work includes testing of nine reinforced concrete slab specimens with dimensions (1700mmx300mmx100mm), six of these slabs were strengthened, two slabs were repaired with carbon fiber reinforced polymer (CFRP) strips and one specimen was tested without strengthening as reference (control) slab for comparing the performance of CFRP strengthened or repaired slabs. The experimental variables considered in the test program include the location, quantity, shape and dimensions of CFRP sheets. All the reinforced concrete slab specimens were designed of the same dimensions and reinforced identically to fail in flexure. All slabs were tested in simply supported conditions subjected to central concentrated load. The experimental results show that the ultimate loads are increased by about (8-64%) for the slabs strengthened with bonded CFRP sheets with respect to the unstrengthened reinforced concrete slab (control slab). Three-dimensional nonlinear finite element analysis has been used to conduct the numerical investigation of the general behavior of strengthened slabs. ANSYS (Version 13.0) computer program was used in this work. Eight-node brick elements (SOLID65) are used to represent the concrete and three dimensional shell elements (SHELL 41) are used to represent the CFRP strips in the finite element analysis model. Perfect bond between the concrete surface and the bonded CFRP sheets is assumed.