you will not be responsible for anything other than her rent - but do not do it!!! there are plenty of ways to rent other than using a guarantor, for example, make her go and see her local housing department and they will have a list of landlords that she can use and other advice. you do realise that if she defaults or becomes incapable of paying, say, £600 for a year that it will cost you £7200? and if you do not have whatever her months rent is as spare cash at the moment that you will not be able to pay your rent/mortgage and/or bills.......as the guarantor WILL chase you. my son asked me to do this and much as i love him (and he works, is at uni etc.) i WILL not put my home at risk for anybody. blood is thicker than water, but that doesn't mean that your sister won't screw you over if it means saving herself. think about what you are doing.......