In this paper, a reliability-based computational algorithm was developed and coded into a computer program, P-UASLOPE, for design of a row of equally spaced drilled shafts to stabilize an unstable slope while achieving the required target reliability index with minimum volume of drilled shafts. The Monte Carlo simulation technique was used in the previously developed deterministic computational program, in which the limiting equilibrium method of slices was modified to incorporate the arching effects of the drilled shafts in a slope. Uncertainties of soil parameters in the slope were considered by statistical descriptors, including mean, coefficient of variance, and distribution function. Model errors of the semi-empirical predictive equation for the load transfer factor for characterizing the soil arching effects were considered by statistics of bias. A total of 41 cases of 3-D finite element simulation results were used to determine the statistics of bias. Two design examples, one is a two-layer slope and the other one is an actual failed slope, were given to demonstrate the use of P-UASLOPE program for optimized design of drilled shafts reinforced slope system to achieve the most economic combination of design variables (i.e., location, spacing, diameter, and length of drilled shafts) to satisfy the design requirements in terms of target reliability index and the structural performance of the drilled shafts. A single value of factor of safety chosen in the deterministic approach may not yield the desired level of reliability as uncertainties of soil parameters and model errors cannot be accounted for systematically. Copyright © 2013 John Wiley & Sons, Ltd.