In conventional compressed sensing (CS) multi-slice Cartesian 2D imaging, the undersampling is performed along phase-encoding direction only, leading to coherent 1D aliasing that significantly limits the effectivess of CS for acceleration. This study proposes a multi-slice CS reconstruction method to take advantage of extremely augmented sampling incoherence created by orthogonally alternating phase-encoding directions among adjacent slices. The multi-slice CS approach was evaluated with single-channel brain T1W and T2W datasets. The results demonstrate significant improvements with both pseudo-random and uniform undersampling. This new method will also greatly augment the existing 2D CS parallel imaging technqiues for very high acceleration.