An apparatus for estimating bio-information is provided. The apparatus includes: an ultrasound image acquirer configured to acquire ultrasound images of an object; a pressurizer configured to apply pressure to the object to occlude a blood vessel; and a processor configured to estimate a change in a diameter of the blood vessel using the ultrasound images acquired by the ultrasound image acquirer before and after an occlusion of the blood vessel, and estimate bio-information based on the estimated change in the diameter of the blood vessel.