An apparatus for estimating oxygen saturation is provided. The apparatus may include a sensor configured to measure optical signals of multiple wavelengths based on emitting multi-wavelength light onto an object; and a processor configured to: determine a section of the optical signals for estimating the oxygen saturation based on a difference between at least two optical signals among the optical signals of the multiple wavelengths; and estimate the oxygen saturation based on the optical signals of the multiple wavelengths in the section.