Resource-constrained project scheduling problem (RCPSP) is one of the most important problems in the context of project scheduling. Considering a single objective, such as makespan minimization, net present value minimization or cost minimization has been the cornerstone of most studies done so far. At the other hand, taking this problem into account as a multi objective one has not been well studied. In this paper, a bi-objective model of RCPSP is presented. The first objective is makespan to be minimized, and the second one, a recently developed measure, is robustness maximization aimed at floating time maximization to make scheduling more reliable. The problem formed in this way is an NP-hard one forcing us to use simulated annealing algorithm to obtain a global optimum solution or at least a satisfying one. Finally, we have illustrated our new algorithm using a numerical example with different weights for robustness. (As an example, when robustness weight is zero, the problem will be solved as a makespan objective.)