You can very well demat private company shares also ,it's on the need and requirements of company ,depending on folio number , generally you have to enter into contract with RTA and then sign up through that RTA for ISIN generation by Master Creation form ,you can check the process at following link ( It's a PPT by Karvy)
Thank you all for your replies. Kindly also let me know is it mandatory to dematerialise the private company shares? Kindly refer to the section wherein it is stated?