Novel benzo [b,f] thiepin derivatives possessing strong anti-flammatory action and presenting few adverse reactions, of the formula (I) ##STR1## wherein R represents a fluorine atom, or a trifluoromethyl or 1-5C lower alkoxy group, and R.sub.3 and R.sub.4 each represent a 1-4C lower alkyl group or R.sub.3 and R.sub.4 together with the adjacent nitrogen atom to which they are attached form a heterocyclic group. Pharmaceutical compositions comprising an anti-inflammatory effective amount of the compound according to formula (I) in the presence of an inert carrier.