A method that optimizes the parameters of the Least Squares Support Vector Machines (LS_SVM) by using Bacterial Colony Chemotaxis is presented.This optimization algorithm is used to optimize the target function by analogy to the way bacteria react to chemoattractants in concentration gradients. This method greatly improves the efficiency of LS_SVM’s parameters selection, and with the parameters selected, the classification result for the testing samples is the optimum. It avoids the disadvantage of manually specifying the parameters, and also scales down the optimisation time.