There is disclosed a mesomorphic compound represented by the following formula (I): ##STR1## wherein A.sub.1 denotes a single bond, ##STR2## denotes ##STR3## X denotes hydrogen, a halogen or cyano group; Y denotes oxygen or sulfur; R.sub.1 and R.sub.2 respectively denotes a linear or branched alkyl, alkoxy, alkylcarbonyloxy, alkoxycarbonyl or alkoxycarbonyloxy group each having 1-18 carbon atoms and each capable of having a substituted of chloro, bromo, cyano, alkoxy or akoxycarbonyl group; and B denotes ##STR4## A ferroelectric liquid crystal composition comprises at least two mesomorphic compounds including at least one mesomorphic compound represented by the formula (I). A ferroelectric liquid crystal device is constituted by disposing the ferroelectric liquid crystal composition between a pair of substrates.