In this study, a mathematical model was considered to determine the optimal prices of main and auxiliary products in a complementary relationship sold by one company. This research investigated managerial implications by producing the difference between the optimal price considering the complimentary relations and the one not considering it. The differences between those two prices, that is, the biases were provided by the mathematical model and were shown by inserting the hypothetical numbers for the variables. If there is a complementary relationship, it should be considered in estimating the prices. And then unbiased optimal prices can be estimated. We examined how big its difference between the price considering the complimentary relationship and the one not considering it is. We also investigated how it changes according to the change of the components. Its difference is shown to increase, as weight and complementary factor increase. That is, the effect of the price of other product on the demand of its own product increases. Both prices of its own product and other products affect its demand, and then the total effect of prices increases the difference between optimal prices. In addition, the differences of optimal prices between main and auxiliary products were investigated. In the auxiliary product, the differences of optimal prices are bigger. So it shows asymmetric differences. Finally, the limitation of the study and the suggestions for the further study are provided.