Internal stress field in a severely deformed aluminium with ultrafine grained microstructure has been studied by convergent-beam electron diffraction (CBED) technique in transmission electron microscopy (TEM). A commercial purity aluminium (99.1%Al) sheet was highly strained by the accumulative roll-bonding (ARB) process to evolve an ultrafine grained structure. Higher-order Laue zone (HOLZ) lines in the incidence disk of the [112] zone axis have been observed at various positions within an identical ultrafine grain. The key finding is that the HOLZ line pattern taken from the vicinity (similar to 50nm) of the grain boundary (lamellar boundary) looses (011) mirror symmetry, whereas the pattern from the grain centre has the symmetry. The former and the latter represent the existence of a large non-hydrostatic stress field and a small internal stress field, respectively. The magnitude of the internal stress becomes larger with approaching to a grain boundary.