Electrochemical Machining (ECM) is a machining tool that uses the principle of electrolysis, so that it can be used for machining of electrical conductor materials. ECM has the advantage of being able to do machining of hard materials and complicated shapes. Previous research has examined ECM machining with various tool shapes, but the results obtained have not been optimal, so more in-depth research is needed so that the optimal machining results are obtained. This study aims to optimize the results of MRR skin, overcut and taper from the laboratory scale of ECM machining holes on aluminum 1100 in masking and non-masking workpieces due to gap control using a perforated brass electrode. The gap variations used were 0.5, 0.75 and 1 mm with a flow rate of 2.5 lpm, a concentration of 10% (w/v) NaCl, a voltage of 10 volts and a processing time of 200 seconds. From the machining results it is known that the smaller the gap, the greater the MRR and overcut that will be generated. The biggest average MRR is 0.5 mm gap, which is 3.435 x 10-3 g /s with 43% overcut on workpieces that do non masking and 3.311 x10-3 gr/s with 33% overcut on masking. MRR and the overcut value on non-masking workpieces is greater than the masking workpiece, it is affected by the current that appears on the non-masking workpiece is greater because it spreads to the surface of the workpiece. In the masking workpiece results have a different phenomenon from each variation of the slit provided, the smallest value of the masking workpiece is 16.170 at a gap of 0.5 mm, the smallest value of the non masking workpiece is 36.870 at a gap of 0.5 mm.