Accurate blood typing is required before transfusion. A number of methods have been developed to improve blood typing, but these are not user-friendly. Here, we have developed a microfluidic smart blood-typing device operated by finger actuation. The blood-typing result is displayed by means of microfluidic channels with the letter and the symbol of the corresponding blood type. To facilitate the mixing of blood and reagents, the two sample inlets are connected to a single actuation chamber. According to the agglutination aspect in the mixture, the fluids are directed to both the microslit filter channels and bypass channels, or only to the bypass channels. The dimension of the microslit filter being clogged by the red blood cell aggregates was optimized to achieve reliable blood-typing results. The flow rate ratio between two channels in the absence of agglutination was subjected to numerical analysis. With this device, blood typing was successfully performed by seven button pushes using less than 10 mu L of blood within 30 s.