The thermal expansion and magnetostriction of polycrystalline sample of the ErMn6Sn6 intermetallic compound with hexagonal HfFe6Ge6-type structure are investigated in the temperature range of 77 K to above 400 K. The thermal expansion measurement of the sample shows anomalous behavior around its TN¼340 K. The isofield curves of volume magnetostriction also reveal anomalies at paramagnetic–antiferromagnetic and antiferromagnetic–ferrimagnetic phase transitions. In the antiferromagnetic state, the transition to ferrimagnetism can be induced by an applied magnetic field. The threshold field for the metamagnetic transition Hth increases from 0.18 T at 84 K to about 1 T around 220 K, and then decreases monotonously to TN. This behavior is well consistent with that observed earlier on magnetization curves attributed to exchange-related metamagnetic transition rather than the anisotropy-related one. Furthermore, the low Hth values suggest that the Mn–Mn coupling in ErMn6Sn6 is not so strong. The experimental results obtained are discussed in the framework of twomagnetic sublattice by bearing in mind the lattice parameter dependence of the interlayer Mn–Mn exchange interaction in this layered compound. From the temperature dependence of magnetostriction values and considering the magnetostriction relation of a hexagonal structure, we attempt to determine the signs of some of the magnetostriction constants for this compound.

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