A blood analyzer has a light emitter for emitting light to an analysis sample which is a mixture of a blood specimen and a reagent. It also has a light receiver for receiving light of a plurality of wavelengths from the analysis sample over time, and for acquiring data of the amount of the received light corresponding to each of the wavelengths at a plurality of points of time. A selector selects the data corresponding to one of the wavelengths, based on the change of the amount of received light over time in the data acquired by the light receiver. An analysis section analyzes a characteristic of the blood specimen using the data which are selected by the selector. A blood analyzing method is also described.