The invention relates to liquid compositions for production of soft sustained-release capsules. According to the invention, the sustained release of the active agent is obtained by in situ formation of a matrix, more or less consolidated and biodegradable, by physical modification of the capsule contents on coming into contact with digestive juices on the opening thereof. The above leads to a release time of more than one hour for the active agent previously dissolved or dispersed by means of solvents, said release being modulated by addition of appropriate adjuncts. The invention further relates to a method for production of said liquid compositions. The above finds application in the pharmaceutical, cosmetic and dietary fields.