Fact gathering means generating rule base from available numerical data. The intelligence of a fuzzy system lies in its rule base. Number of rule base generation methods are used for fuzzy system such as neural networks, as hybrid learning, genetic algorithms, Wang & Mendel Approach, biogeography based optimization approach and particle swarm optimization found in the literature. Designing fuzzy systems is an optimization problem. This paper presents a recent nature-inspired algorithm named Ant Colony Optimization (ACO) approach for automatic generation of optimized fuzzy rule base from available numerical data i.e. fact gathering.