Determination of blood flow changes will be helpful for evaluation of tumor prognosis and therapy. Our study is to develop an in vitro hemodynamic phantom model, which allows us to show the feasibility of using near infrared spectroscopy (NIRS) to determine flow changes as a dynamic imaging modality to monitor tumor responses to therapy. In the hemodynamic phantom model, both single and multiple, transparent, plastic tubes were used to pass through a cylindral glass chamber. The chamber was filled with either an Intralipid solution or a soft gelatin phantom, while the tube or tubes were pumped with either an Intralipid-ink mixture or animal whole blood to simulate the tumor vasculature. The Intralipid solutions that were filled in the chamber and tubes had optical scattering and absorption properties similar to those of tumor tissues and tumor vasculature. A single-channel, broadband, NIRS system with a tungsten light source and a CCD-array spectrometer was used to quantify the changes in optical density (OD) of the intralipid-ink mixture with variations in flow rate and concentration. A single-exponential curve fit has been used to determine the time constant (τ) from the change in OD to estimate the flow rate. The obtained preliminary results show a strong correlation between changing rates of concentration and flow; a multivariable dynamic mathematical model may be also established to relate changes of Hb, HbO and blood volume with blood flow.