Accordingly, the present invention provides a process for preparing polyglycerol from crude glycerol, wherein the crude glycerol having a glycerol content from about 60 to about 90%, soap content from about 10 to about 15% and methanol content from about 5 to about 20%, the process includes the steps of (a) heating the crude glycerol that contains soap to an elevated temperature for a certain reaction time, (b) acidifying the crude polyglycerol with mineral acid at a specific temperature and (c) centrifuging the acidified crude product obtained from step (b) at specific temperature for a certain duration of time.