This paper describes the performance of the twin-fluid type micro-atomizer designed with internal-impinging mechanisms. This micro-atomizer is fabricated via MEMS bulk micro-machining processes. It is designed with three micro channels for the liquid and gas supply. The orifice hydraulic diameter of the micro atomizer is 45μm. Results show that the velocity profile of the spray is essentially the jet structure with its peak velocity of 6m/s in the central region of the spray jet. Flow visualization through a microscope shows that the liquid becomes a meniscus over the nozzle outlet for the single-fluid injection if the water flow rate is less than 0.4ml/min. It implies that the effect of the surface tension is stronger than the inertial force under the low flow rate range. The liquid becomes a single stream pattern when the flow rates of the single-fluid injection are increased from 0.4ml/min to 1.0 ml/min. However, the liquid becomes the spray flow with a cone angle when the gas flow is supplied to the micro-atomizer even under low gas pressure. For example, at the gas pressure of 2bar, the spray has a cone angle of 40°. This phenomenon could be related to excitation of the helical mode due to the impingement of the gas flow at a higher Reynolds number. It results in the favorable condition for atomization processes. Hence the production of fine spray with Sauter mean diameter of 5μm is achieved by the twin-fluid micro-injection under the gas pressure of 5.0bar and the liquid flow rate of 0.1ml/min, a performance better than the micro atomizers reported in the literature.