This paper presented an electromagnetic cantilever generator (EMCG) of high energy density with high-permeability magnetic materials for harvesting ambient vibrational energy. We utilized a flexible cantilever connecting with a pair of magnets on the free end, and the coils with high-permeability magnetic materials are set right in front of the magnets. The electrical power is produced from coils based on electromagnetic mechanism. The high-permeability magnetic materials amplify the magnetic flux change, making it appropriate for vibrational energy harvesting at a resonant frequency. The gap between magnets and coils is discussed since it will influence the output of the system. Under the resonant frequency of 21 Hz, a peak-to-peak open-circuit voltage of 4.5 V is obtained at an acceleration of $1g$ with the gap of 2 mm. And a maximum value of 160 mW is measured at a load resistance of $4\ \Omega$, this translate into a power density of 32 mW/cm3, which can be a promising way to solve the power supply problem.