The self-assembly of diblock copolymer mixtures (A-b-B/A-b-C or A-b-B/B-b-C mixtures) subjected to cylindrical confinement (two-dimensional confinement) was investigated using a Monte Carlo method. In this study, the boundary surfaces were configured to attract blocks A but repel blocks B and C. Relative to the structures of the individual components, the self-assembled structures of mixtures of the diblock copolymers were more complex and interesting. Under cylindrical confinement, with varying cylinder diameters and interaction energies between the boundary surfaces and the blocks, we observed a variety of interesting morphologies. Upon decreasing the cylinder''''s diameter, the self-assembled structures of the A15B15/A15C15 mixtures changed from double-helix/cylinder structures (blocks B and C formed double helices, whereas blocks A formed the outer barrel and inner core) to stacked disk/cylinder structures (blocks B and C formed the stacked disk core, blocks A formed the outer cylindrical barrel), whereas the self-assembled structures of the A15B7/B7C15 mixtures changed from concentric cylindrical barrel structures to screw/cylinder structures (blocks C formed an inside core winding with helical stripes, whereas blocks A and B formed the outer cylindrical barrels) and then finally to the stacked disk/cylinder structures. In contrast, increasing the interaction energy between the boundary surfaces and the blocks, the self-assembled structures of the A15B15/A15C15 mixtures changed from stacked disk structures (sequence of alternating A and BC disks) to BC stacked sphere/cylinder structures (the core was connected by B and C spheres in an alternating sequence) and then to the stacked disk/cylinder structures, whereas the self-assembled structures of the A15B7/B7C15 mixtures changed from stacked disk structures (sequence of alternating of A, B, and C disks) to catenoid/cylinder structures (B blocks formed a bottleneck structure connecting the separate cylindrical BC domains) and then to the stacked disk/cylinder structures. Moreover, we have analyzed the self-assembled structures in terms of chain conformation and given the chain packing models for various self-assembled structures.