Ti50Ni50 thin foils up to 10μm thickness are successfully fabricated from 100μm thickness thin plates using chemical machining. Ultrasonic agitation is applied to enhance the chemical etching process with mixed solutions of HF/HNO3/H2O. The higher the HF/HNO3 volume ratio in the solution, the higher the etching rate and the smoother the surface will be. Thin foils can also be fabricated with the electropolishing process but with a much slower etching rate. Foil thickness by these processes can only be approximately 10μm due to the side-etching effect. The martensitic transformation peaks of thin foils shown on the DSC curve are broader for a thinner sample due to the effect of thermal resistance in the DSC sample pans. The enthalpy of transformation also decreases while the foil thickness is reduced due to the effect of the foil surface energy and the energy of plastic deformation.