By means of a gel-growth method well habitted orthorhombic Ca-tartrate single crystals grow several millimeters in size. The dominant faces developed are {110} and {101}. It has been found that an extremely diluted HCI solution of HCI : H₂O=1: 500 is an excellent dislocation etchant for the Ca-tartrate crystals. With etch pits the crystallographic orientation and face indices are assigned easily, because their shapes and orientations are proper and characteristic to the individual faces. On the matched crystal faces cut by cleavage there occur surface structure revealing traces of modification due to dislocations. It has been found that the cleavage plane produces extended giant-step-line structures at passing a swarm of spiral dislocations. Some of them are over 300 nm high and can be observed easily by optical microscopy. This would provide an evi-dence that the lattice shift in the bulk due to spiral dislocation is released as a step structure on the free surface.