For ultrasonic molecular imaging, evaluation for molecular expression has been discussed for decades. However, there is no method to quantify the precious expression level of molecules using ultrasonography. To solve this problem, it is important to understand the chemical kinetics between targeted microbubbles (TMBs) and target molecules as a fundamental study. Therefore, we construct the system composed of a quartz crystal microbalance (QCM) sensor and flow system. By using the proposed system, we evaluated the adsorption rate and amount of TMBs to target molecules and investigated how these parameters relate to the number density of TMBs.