An apparatus for estimating bio-information is provided. According to an embodiment of the present disclosure, the apparatus for estimating bio-information includes: a first sensor configured to measure a first pulse wave signal of a first wavelength and a second pulse wave signal of a second wavelength from an object; a second sensor configured to measure at least one of a force or a pressure applied to the object; and a processor configured to: generate an oscillometric waveform envelope based on the first pulse wave signal of the first wavelength and the at least one of the force or the pressure applied to the object; obtain a feature value from the oscillometric waveform envelope; predict a size of a measured blood vessel based on the second pulse wave signal of the second wavelength; correct the feature value based on the size of the measured blood vessel; and estimate the bio-information based on correcting the feature value.