Cyclic deformation behavior of double-slip oriented Cu single crystals with a stress axis in the [034] direction was investigated under plastic strain control mode for a shear strain amplitude range of 1 x 10-4 to 5 x 10-3. Dislocation structures in the tested samples were observed using a transmission electronic microscope. It has been found that the effect of the operation of critical slip in these [034] crystals on cyclic responses and dislocation structures is nearly the same as that of increase in strain amplitude. The nucleation stress and number of cycles for PSB formation at each specific strain amplitude in the double-slip oriented crystals were found to be both considerably lower than those observed in single-slip oriented crystals. This observation is in a good agreement with the Kuhlmann-Wilsdorf and Laird analysis, in that the formation of PSBs is associated with glide behavior on the secondary slip system. A dislocation "cord" structure has also been observed and is believed to be caused by the operation of the cross-slip system during cyclic deformation. Labyrinth wall structures were found to form with increase in strain amplitude by the operation of critical slip and cross-slip systems. However, the formation of labyrinth structure was suppressed by the coplanar slip at high strain amplitudes.