High temperature superconductor YBa2Cu3Ox (YBCO) and Bi2Sr2CaCu2Ox (BSCCO) thin film microstrips were prepared by argon ion beam etching down to a geometrical width W(g)approximate to250 nm. A study of transport properties of the superconducting microstrips showed that due to the interaction of accelerated argon ions with the superconductor film the edges of microstrips are damaged to a depth DeltaWapproximate to85 nm. The effective width of YBCO microstrip W-ef = W-g-2DeltaWapproximate to80 nm is able to transmit a critical current density above 20 MA/cm(2) at a temperature of 30 K and a zero external magnetic field. The critical current density of similar BSCCO microstrips was several times smaller. (C) 2003 Elsevier Science B.V. All rights reserved.