We found unidirectional nanocracks in unidirectionally twinned films ofYBa2Cu3O7−&dgr;onNdGaO3which are normal to the twin planes. In 70–250 nm thick films, transmission electron and atomic force microscopy show that these unidirectional nanocracks are found to be 1–2&mgr;mapart and have 2–4 nm width. Microbridges that cross these nanocracks behave as natural Josephson junctions. They show Shapiro steps under microwave irradiation and suppression of the critical currentIcin magnetic fields. A very large in-plane anisotropy of the resistivities andIcwas observed and this was correlated with the nanocracks orientation, length, and film thickness. The observed anisotropy ofIcnearTcis shown to be consistent with ad+iswave symmetry of the order parameter inYBa2Cu3O7−&dgr;.©1998 American Institute of Physics.