A tuned liquid column damper (TLCD)—devised for vibration mitigation of high structures—is a passive damper categorized as a dynamic absorber. A magnetic fluid is a smart, colloidal, and strongly magnetizable fluid, and is composed of a base liquid, ferromagnetic particles, and a chemically adsorbed surfactant. Using a magnetic fluid as the working fluid of a TLCD can improve and change the TLCD into a novel semiactive damper called a tuned liquid column damper with a magnetic fluid (MF-TLCD). The natural frequency of a MF-TLCD can be changed by applying magnetic field. This novel damper can be used as an effective vibration suppression mechanism for building structures. In this study, we present the equation of motion of a MF-TLCD, and solved it numerically using a 4^th-order Runge-Kutta method. Using the numerical results, we demonstrate the frequency responses of a MF-TLCD and the effect of the magnetic field on the natural frequency of a MF-TLCD. In addition, we compare numerical results with experimental results, and show that they are coincident qualitatively.