The invention relates to a leaf assembly (102) for a multi-leaf collimator, comprising a leaf frame (104) and a plurality of leaves (106) for shielding beams (108) from a selected area, wherein the leaves (106) are arranged sideways and adjacently in the leaf frame (104) for shielding beams (108) being emitted from a radiation source (110) located above the assembly (102), wherein each leaf (106) is mounted in the leaf frame (104) displaceably in an adjusting direction (112) being oriented perpendicularly related to said beams (108), and wherein the leaf frame (104) provides a linear guidance (114) for each leaf (106) within the adjusting direction (112), being designed in a such a way that the leaf frame (104) is adapted to allow for lateral movement of the leaves (106) superposing said linear guidance (114), thus allowing mutual abutting of the leaves (106). Furthermore, the invention relates to a multi-leaf collimator comprising two leaf assemblies (102) according to the invention, wherein the assemblies (102) are arranged to face each other within the adjusting direction (112). The invention is based on the objective of designing a leaf assembly (102) for a multi-leaf collimator and a multi-leaf collimator in such a way that the occurrence of leak-age radiation may be diminished.