The composites of thiourea with lithium niobate (a), with lead titanate (b) and with barium titanate (c) (in all cases thiourea part was 0.90) have been investigated close to structural phase transitions in thiourea using dielectric spectroscopy. The hysteresis increase and temperature decrease of the ferroelectric phase transition from phase I to phase II for all investigated compounds as compared with similar properties of the polycrystalline thiourea were found. The most decrease in the transition temperature was observed for the (c) composite. The results were analyzed in the framework of the Landau-Ginzburg theory.