Air traffic demand forecasting plays the important role for developing the efficient operating strategy. This study employed supervised back-propagation neural networks to develop a simple MATLAB computer program in order to forecast air passenger demand from Japan to Taiwan. All input variables were collected by literature survey, market analysis and preliminary evaluation. The factors which influence air passenger market were analyzed in detail by deleting method, adding method, and contribution graph. The following 8 variables were selected as the input variables to establish the forecasting model: population in Japan, employed population in Japan, per capita income in Japan, GDP in Japan, GNP in Japan, foreign exchange rate, flight movement from Tokyo (NRT) to Taipei (TPE), per capita income in Taiwan. The novel BPN model can accurately forecast air passenger demand with an extremely low Mean Absolute Percentage Error of 0.34%. The results reveal that flights from Tokyo (NRT) to Taipei (TPE), PCI in Taiwan, and foreign exchange rate are the three most important factors for air passenger volume.