We have studied critical currents of YBa2Cu3O7 step-edge junctions with dif
ferent step-line angles with respect to the major axes of SrTiO3 (100) subs
trates. Measurements of the junction critical current indicated a periodic
modulation with the step-line angle: maxima near 0 degrees and 90 degrees d
egree and minima near 45 degrees and 135 degrees. These results are in qual
itative agreement with d-wave coupling superconductivity at the step-edge g
rain-boundary of the junctions.