This paper reports a polymer micro-pen with an integrated microchannel and a sample reservoir, which can be actuated by Lorentz force induced on an integrated metal actuator for biological assay patterning. The length, width and thickness of the micro-pen are 500μm, 120μm and 6μm, respectively. The fabricated micro-pen is successfully deflected by electromagnetic force from external permanent magnets which generates a magnetic field of 0.2T. Spring constant of the micropen is analytically estimated as 1.9N/m and the measured resonance frequency is about 7.3 kHz. The microchannel formed on this polymer micro-pen is 15μm wide and the sample reservoir is 500μm thick in the area of 300μm×300μm. Red ink is pulled up to the end point of the microchannel from the reservoir by capillary force. A red-ink-dot in diameter of 11μm has been placed on paper by the fabricated micro-pen. This demonstrates a sub-picoliter patterning of biological assay is possible.