usually a guarantor is somebody who owns property in the city to accept responsibility for the rented unit should the tenant not pay rent, if there are any damagses, and to cover various additional costs as detailed in specific clauses.

a rental-insurance (seguro-fiança) is a type of insurance that covers up to three months of past due rent in case the tenant falls behind and eviction proceedings are initiated - this contract is the most common option among foreigners who cannot get a local co-signer - a policy cost about one to two months of rent per year, and it is paid monthly by the tenant to the insurance company.

one of the most popular companies that offers rental insurance is porto seguro, posting an application form on this page, and requiring a cpf.