The standardized two-microphone method is widely established for determining normal-incidence acoustic properties. Instead of numerous low-frequency usages, only a few high-frequency applications are reported. This paper provides insights into implementing the two-microphone method in an impedance tube based on two MEMS microphones for a frequency range of 5 kHz to 50 kHz. In doing so, we encountered technical issues associated with the MEMS microphone utilization and the high-frequency application. These issues can be addressed by implementing a modified method, in which an adaptive stepped sine excitation and a curve-fitting technique were applied. The modified method was validated by using three classical tube terminations, e.g., closed, open, and horn. The measured data of these terminations are in line with their analytic solutions. In conclusion, when proper concerns are taken, the acoustic properties up to the lower ultrasonic range can be determined using the modified two-microphone method in an impedance tube based on two MEMS microphones.