To investigate the toxicological effects of nanomaterials, experimental studies on the absorption and accumulation in organisms are of broad interest. In the present study, Caenorhabditis elegans (C. elegans) was used as a ''model'' organism to investigate the bioaccumulation and toxicological effects of engineered copper nanoparticles with a scanning technique of microbeam synchrotron radiation X-ray fluorescence (m-SRXRF). The adult hermaphrodite is anatomically simple with 959 somatic cells and 1 mm in length. The mapping results of the whole organism indicate that the exposure to copper nanoparticles can result in an obvious elevation of Cu and K levels, and a change of bio-distribution of Cu in nematodes. Accumulation of Cu occurs in the head and at a location 1/3 of the way up the body from the tail compared to the un-exposed control. In contrast, a higher amount of Cu was detected in other portion of worm body, especially in its excretory cells and intestine when exposed to Cu 2+ . The results compared well with total Cu levels in nematodes, which were 4.10 AE 0.54, 12.32 AE 0.49 and 5.22 AE 0.63 mg g À1 dry weight for the PBS, Cu 2+ and Cu nanoparticle groups, respectively, measured by ICP-MS. The nondestructive and multi-elemental m-SRXRF provides an important tool for mapping the elemental distribution in the whole body of a single tiny nematode at lower levels.