In general, chemical processes (CP) are designed with the use of inaccurate mathematical models. Therefore, it is important to create a chemical process that guarantees satisfaction of all design specifications either exactly or with some probability. The paper considers the issue of chemical process optimization when at the operation stage the design specification should be met with some probability and the control variables can be changed. We developed a new formulation of the two-stage optimization problem (TSOP) with chance constraints. On the basis of this formulation and approximate transformation of chance constraints into deterministic ones the iteration method of solving the TSOP with chance constraints is devised. (C) 2011 Elsevier Ltd. All rights reserved.