Bicrystalline micropillars (BCMs) involving several grain boundaries along the pillar axis were fabricated in an oxygen-free copper sample by focused ion beam milling. These pillars were compressed using a nanoindenter to investigate slip transfer across grain boundary (GB). Referring their stress-strain (SS) curves, the possible slip systems were resolved from scanning electron microscope images after deformation and GB interaction criteria with the Schmid factors (SFs) of each grain and the geometric relationship of intersections between slip planes and GB. The quite different SS behaviors were observed in the BCMs, of which one was the unstable elastic-almost perfect plastic deformation due to large strain bursts and the other was work-hardening accompanying several small strain bursts. The 1%-proofs obtained from SS curves were found to be roughly correlated with the GB interaction criteria the author already proposed except some GBs.