Is it permissible for me to marry the daughter of my mother's paternal uncle?

A person's paternal uncle is an uncle to all of his descendants, because the uncle is the brother of the father or grandfather. Thus, the mother's paternal uncle is considered an uncle to her children, and his children are paternal cousins to the children of that mother. Based on this, the daughter of the mother's paternal uncle is considered your paternal cousin, and marriage to her is permissible because she is not among the mahram (unmarriageable kin).