In this paper we develop the concept of a living optical phantom that uses engineered tissue as a phantom for calibration and optimization of biomedical optics instrumentation. With this method, the effects of biological processes on measured signals can be studied in a well controlled manner. To demonstrate this concept, the effects of cellular remodeling of a collagen matrix on the optical scattering properties were investigated using optical coherence tomography (OCT). Living optical phantoms of the vascular system were created by seeding smooth muscle cells in a collagen matrix. The optical scattering properties (scattering coefficient μs and effective anisotropy factor geff) were extracted from OCT images through mathematical processing. We found that the scattering coefficient of a remodeled matrix was generally higher than that of an unmodified matrix. The results indicate that OCT may provide meaningful information on how cellular remodeling of an extracellular collagen matrix changes its scattering properties. More broadly, we believe that making such optical measurements on living optical phantoms can help define the potential of biomedical optics technologies for studying biological systems.