[en] Genetic algorithm is a stochastic optimization method which has been used in many research and engineering field in recent years. Core loading pattern of two research and test reactors, the High Flux Engineering Test Reactor and Ming Jiang Test Reactor, have been tackled using the GA optimization. Parameters have been tested and two new techniques, Imaginary Core Technique and Symmetric Mutation Operator, have been used in our GA program. As a result, conversion ratio and average cobalt output have been increased about 10% than the expert's LP. (author)