This paper presents a new co-operative search approach, the ant colony optimisation paradigm, for the optimal design of batch chemical processes and illustrates it by solving (1) the combinatorial optimisation problem of multiproduct batch scheduling and (2) the continuous function optimisation problem for the design of multiproduct batch plant with single product campaigns and horizon constraints. The ant algorithm is simple to implement and results of the case studies show its ability to provide speedy and accurate solutions.