Structures designed following the code limitations and factors of safety are expected to achieve a reasonable afety. Reliability can be defined as the probability that a structure will not fail while it performs its intended function. It can be used as a highly efficient tool for calibrating code equations in order to maintain a homogenous reliability index beforeand after strengthening. The main objective of this research work is todetermine reliability indices for reinforced concrete (RC) beamssubjected to flexural failure before and after strengthening using MonteCarlo simulation. Also, an experimental work on reinforced concrete beams strengthened with carbon fiber reinforced polymer (CFRP) plateswas made in order to compare between experimental results and analytical model (ECOP code of practice for FRP). The following parameters were considered: Shear span to effective depth ratio, live load to dead load ratio, working moment to moment apacity ratio and number of layers of CFRP plates (1, 2 and 3layers). Software was developed by the author to get a wide range of results considering the prescribed parameters. The results indicated that the reliability of reinforced concrete beams remarkably differs after strengthening. Also, the reliability indices are significantly affected by beam geometry, loading scheme, FRP thickness and live to dead load ratios. The reliability analysis was carried out based on the guidance provided by Egyptian code of practice for the use of fiber reinforced polymer (FRP) in the construction fields.