In Texas, a father can file for sole custody of his child based on the mother being unfit to raise the child. Because Texas favors splitting parenting time between both parents, as this is most often the best situation for children, if the father proves the mother is unfit, he can acquire sole custody of the child. However, it is up to him to prove to the courts that the mother is unfit and show that the child is better off with him.

File a Petition in Suit Affecting the Parent-Child Relationship form with your local Texas courthouse. This form indicates that you are seeking custody of your child, and it allows you to make requests in regard to the ability of the mother to spend time with the child, such as requesting that she not drink around the child and setting other restrictions.

Gather any documentation you have that shows her behavior is negatively impacting your child. This includes any police reports or medical records that demonstrates injuries to the child while she is with the mother. Document how often the mother sees the child and how your child acts after spending time with her mother. Take pictures of your child's mother engaging in inappropriate activities, if you can. Print emails and text messages between you and your child's mother and play back voicemails that would help your case. The more solid documentation you have, the better your chances of being successful in gaining sole custody of your child.

Take your child to see a counselor and request documentation from the counselor. The counselor can speak for the emotional state of your child, including any damage that may have been caused by her mother. You may also be able to call the counselor to testify as a witness in your case.

Approach the case from viewpoint of seeking the best interest of the child. Avoid attacking the child's mother, but focus on the fact that she is not a good influence on your child. The court does not care what goes on between the parents. The judge looks at what is best for the child involved, so you need to show that living with her mother is not in the child's best interest.

Call other witnesses who can attest to the mother's damaging behavior toward the child, such as neglect and doing drugs or drinking in the child's presence. If you can find members of her family or her friends who are willing to testify, the court will see that these issues truly are a problem, rather than an attempt by you to create the illusion that the mother is unfit.