A liquid crystal substance having a large optical anisotropy value, a low viscosity and a superior compatibility with other liquid crystal compounds at low temperatures and also raising the degree of choice of liquid crystal materials and a liquid crystal composition containing the above substance are provided, which substance is a 4-(trans-4-alkylcyclohexyl)-3',4'-difluorotolan expressed by the formula ##STR1## wherein R represents an alkyl group of 1 to 10 carbon atoms.