This paper presents a microfluidic flow sensor for the detections of velocity and viscosity, especially for ultra-low viscosity applications. An etched optic fiber with the diameter of 9 mm is embedded in a microfluidic chip to couple laser light into the microfluidic channel. An flow induced vibration causes periodic flapping motion of the optic fiber cantilever. Through the frequency analysis, the fluidic properties including the flow rate and the viscosity can be detected and identified. Results show that this developed sensor is capable of sensing liquid samples with the flow rates from 2.5 ml/min to 15.0 ml/min and the viscosities from 0.306 cP to 1.2 cP. In addition, air samples(0.0148 cP) with various flow rates can also be detected using the developed sensor. The developed flow sensor provides a simple and straight forward method for sensing flow characteristics in a microfluidic channel.