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The crystallinity index of compressed microcrystalline cellulose particles has been estimated using 13 C CP/MAS NMR and photoacoustic FTIR. The results indicate a slight initial increase in crystallinity followed by a decrease as the compaction pressure increases. The initial increase is explained as a transformation of strained structures in cellulose particles into more ordered forms as a result of the initial compression. At higher compaction pressures the crystallinity begins to decrease. This change in crystallinity seems to be larger on the tablet surface than in the tablet bulk and even larger at the tablet perimeter surface than on the top or bottom surfaces of the tablet. Our explanation for these findings is that these differences reflect different levels of shearing forces acting on different parts of the tablet during compaction.