Abstract: Isothermal phase transformation diagram was developed for TPA₂O-B₂O₃ -SiO₂-H₂O system at 160#. B-Si pentasil type zeolite was obtained as a pure phase from the reaction mixture with the mole ratio SiO₂/B₂O₃ being 55-80, and we have for the first time prepared the directing agent of this kind of zeolite. It was proved by electron diffraction technique that the colloidal particles of directing agent with the structure of corresponding zeolite framework, which acts as nuclei, dispersed highly and exhibit directing effect powerfully for the crystallization of B-Si pentasi type zeolite. Also some properties of B-Si pentasil type zeolite such as structure of framework, stability to heat and acid, selective absorption to the infrared and adsorption properties have been studied, May be it provides the evidence for opening up the application of this zeolite.