This study investigates the use of Genetic Programming (GP) to model Reinforced Concrete (RC) beam torsional strength. Experimental data of 76 rectangular RC beams from an existing database were used to develop the GP model. The following input parameters, which affect torsional strength, were selected: beam cross-sectional area, closed stirrup dimensions, stirrup spacing, closed stirrup cross-sectional area of one leg, stirrup and longitudinal reinforcement yield strength, stirrup steel ratio, longitudinal reinforcement steel ratio and concrete compressive strength. Moreover, a short review of well-known building codes in relation to the design of RC beams under pure torsion is presented. The accuracy of the codes in predicting the RC beam torsional strength was also compared with the proposed GP model using the same test data. The study concludes that the proposed GP model predicts RC beam torsional strength more accurately than building codes