Abstract: An apparatus for obtaining bio-information may include a pulse wave sensor including a light source and a detector. The light source is configured to emit multi-wavelength light to an object of interest and the detector is configured to detect light reflected from the object. In addition, the apparatus may include a processor configured to obtain a change in volume of a blood vessel based on one or more of quantity of detected multi-wavelength light and absorbance coefficients of respective wavelengths of the multi-wavelength light and obtain bio-information based on the measured change in volume of the blood vessel.