A novel microporous aluminoborate, denoted as PKU-3, was prepared by the boric acid flux method. The structure of PKU-3 was determined by combining the rotation electron diffraction and synchrotron powder X-ray diffraction data with well resolved ordered Cl- ions in the channel. Composition and crystal structure analysis showed that there are both proton and chlorine ions in the channels. Part of these protons and chlorine ions can be washed away by basic solutions to activate the open pores. The washed PKU-3 can be used as an efficient catalyst in the Strecker reaction with yields higher than 90%.