The purpose of the present study is to investigate the applicability of dynamic analysis of static pressure data to in situ monitoring of the contact line between two immiscible flows in a micro slit. By using pressure taps fabricated for both organic and aqueous phases, the pressure difference between the two phases and the pressure fluctuation are observed for parallel flows of hexane and water. Visual observations of the position of the contact line between two phases performed by using an index for width of organic phase flow frequently show that experimental data deviate from simulation data based on the laminar flow model. The analysis of static pressure fluctuation is important in view of the existence of velocity fluctuations at the confluence and the influence of these velocity fluctuations on the overall velocity distribution. Fluctuation components of pressure measurement data are analyzed by using the Welch method. The frequency analysis of hexane-water flow shows a distinctive spectrum intensity in the frequency domain at about 7 Hz. Since a high spectrum intensity results from fluctuations in the overall velocity distribution, it is considered that the features of the spectrogram could be associated with analytical results pertaining to visual observations of the behavior of the contact line. Thus, the dynamic analysis of pressure data is shown to provide dynamic information about two parallel flows which could be associated with the dynamic behavior of the contact line.