Polyglycerin, polyglycerin fatty acid esters, process for their preparation

The present invention relates to a polyglycerol significantly reduced in content of a polyglycerol having a cyclic structure formed by removal of a water molecule from a polyglycerol molecule, and to a fatty acid ester of a polyglycerol having excellent surface activity. 2 mole or more of glycidol and a catalyst are successively added to 1 mole of glycerol for a reaction to obtain a polyglycerol, in which a ratio of Atotal polyglycerol (1)U to Atotal polyglycerol (2) having a cyclic structureU is A70% or moreU/A30% or lessU (the total of both is 100% by weight) in terms of an intensity ratio determined by liquid chromatography/mass spectrometry; and an average polymerization degree "n" is 2 or more. A reaction of a polyglycerol with a fatty acid provides the corresponding a fatty acid ester of the polyglycerol.