Employing differential scanning calorimetry (DSC) and transmission electron microscopy (TEM), the isothermal crystallization process and precipitated phases of Zr41.2Ti13.8Cu12.5Ni10Be22.5 (at%) bulk amorphous alloy were investigated. It is found that the bulk amorphous alloy exhibited a multi-stage crystallization behavior when being isothermal annealed. The precipitated phases are different at various crystallization stages. The experiment results show that the main precipitation phase is body-centered tetragonal (b.c.t) Zr2Cu at the first crystallization stage but primitive hexagonal ZrBe2 at the second stage, confirming that the Zr41.2Ti13.8Cu12.5Ni10Be22.5 bulk amorphous alloy possesses a phase separation tendency during the isothermal annealing processes. The X-ray diffraction (XRD) result validated that the main precipitation phases were Zr2Cu and ZrBe2 when the bulk amorphous alloy was fully crystallized.