As is well known, liquid crystalline polymers often show an electro-rheological (ER) effect. The polymers show a remarkable viscosity increment and a relatively long response time when an electric field is applied. However, for low molecular weight liquid crystals, the ER effect is small although the response time is fast. These facts suggest that the ER effect depends on the molecular weight of the constituent materials. Diglycerol derivatives are designed and synthesized as oligomeric liquid crystals. These materials show considerably large ER effect and short response time. Consequently, it is considered that these derivatives are expected to be useful ER fluids for many industrial purposes.