Electrochemical micromachining (ECMM) is one of the most fruitful non-traditional micromachining processes to machine the intricate shapes and 3D geometries, but the real challenge is to machine microhole in the hard materials like nickel based alloys, titanium alloy, and stainless steel, etc. Machining of Hastelloy by traditional as well as by non-traditional methods is very difficult because of their high resistance to corrosion and unique strength. Hastelloy is a wrought corrosion-resistant alloy. This research paper investigates how optimization studies are carried out on electrochemical micromachining with multi response characteristics based on the TOPSIS method. The process parameters like voltage, electrolyte, and feed rate are optimized with multiresponse characteristic, which includes taper angle, entry and exit overcut. The optimal parameters obtained from this approach indicate that the lower radial overcut and taper angle was achieved with the combination of the electrochemical micromachining, such as 8V, 0.9mm/min feed rate and sodium perchlorate (NaClO4) electrolyte. TOPSIS approach and ANOVA were used to determine the significant parameter for the ECMM. [ABSTRACT FROM AUTHOR]