The crystal structure of NdGaO3 is studied at 100 K and 293 K using synchrotron single crystal data. The NdGaO3 structure belongs at low and at room-temperatures to the orthorhombically distorted perovskite-type (space group Pbnm, Z=4). The analysis reveals that both structures differ considerably in the character of the thermal motions of the cations. The Nd and Ga thermal ellipsoids at 100 K are reorientated compared with those at 293 K. The anharmonic thermal motions of Nd and Ga, determined for 100 K and 293 K, are displayed by 4-rank polar tensors. The thermal anomaly of the physical properties of NdGaO3 seems therefore, to be well reflected by the thermal behaviour of the cations.