Heat engine using oscillating flow in a micro tube is experimentally investigated. Pressure change due to boiling and condensation causes oscillating flow in a micro tube. Rotational work can be obtained from the oscillating flow using piston-crank system. The effects of design parameter such as driving frequency, tube diameter, heating section temperature are experimentally evaluated. As the driving frequency is increased, the indicated work increases, takes a maximum and then decreases at higher driving frequency. Cycle efficiency shows an almost constant value a low frequencies, and then decreases as the driving frequency. Indicated work and cycle efficiency increase as the heating section temperature increases. The present heat engine shows the best performance in a D = 1.0 mm tube.