The　special　properties　of　nanocrystalline　materials　are　generally　accepted　to　be　a　consequence　of　the　high　density　of　planar　defects　(grain　and　twin　boundaries)　and　their　characteristics.　However,　until　now,　nanograin　structures　have　not　been　characterized　with　similar　detail　and　statistical　relevance　as　coarse-grained,　materials,　due　to　the　lack　of　an　appropriate　method.　In　the　present　paper,　a　novel　method　based　on　quantitative　nanobeam　diffraction　in　transmission　electron　microscopy　(TEM)　is　presented　to　determine　the　misorientation　of　adjacent　nanograins　and　subgrains.　Spatial　resolution　of　＜5　nm　can　be　achieved.　This　method　is　applicable　to　characterize　orientation　relationships＇　in　wire,　film,　and　bulk　materials　with　nanocrystalline　structures.　As　a　model　material,　nanocrystalline　Cu　is　used.　Several　important　features　of　the　nanograin　structure　are　discovered　utilizing　quantitative　analysis:　the　fraction　of　twin　boundaries　is　substantially　higher　than　that　observed　In　bright-field　images　in　the　T(M;　small　angle　grain　boundaries　are　prominent;　there　Is　an　obvious　dependence　of　the　grain　boundary　characteristics　on　grain　size　distribution　and　mean　grain　size.