We have designed and tested a superconducting coplanar waveguide bandstop filter. At a center frequency of 2.84 GHz, a 94% bandwidth low-pass Chebychev design resulted in a filter with less than 0.5 dB in the passband and more than 40-dB insertion loss in the stopband at 35 K. The filter was fabricated by dry etching a laser ablated YBa/sub 2/Cu/sub 3/O/sub 7/ layer on a LaAlO/sub 3/ substrate. Using a cold-wafer probe, accurate, calibrated measurements on the filter and individual lines sections were carried out.