An apparatus for monitoring a physiological condition includes a signal-acquiring unit, an inflating-deflating unit, and a central processing system electrically coupled to the signal-acquiring unit and the inflating-deflating unit. The signal-acquiring unit is used for acquiring a first standard pulse signal and a first reactive hyperemia pulse signal at a specific part of a living being. The inflating-deflating unit is used for selectively inflating and deflating the specific part. The central processing system is capable of transforming the first standard pulse signal to a second standard pulse signal and transforming the first reactive hyperemia pulse signal to a second reactive hyperemia pulse signal using a nonstationary and nonlinear transfer function, respectively, to determine an endothelial function coefficient according to the second standard pulse signal and the second reactive hyperemia pulse signal, thus to analyze a physiological condition of the living being.
