The ban is part of a bill to revamp the state's Child Protective Services agency. It passed 135-6 with two abstentions and now heads to the Senate.
"It is our responsibility to make sure that we protect our most vulnerable children, and I don't think we are doing that if we allow a foster parent that is homosexual or bisexual," said Republican Rep. Robert Talton, who introduced the amendment.
Also Wednesday, another state took a step in the other direction regarding same-sex couples' legal rights. Connecticut's legislature passed, and Republican Gov. M. Jodi Rell signed into law, a measure offering.
If the Texas bill becomes law, it would be the only state to prohibit homosexuals and bisexuals from becoming foster parents, according to the American Civil Liberties Union Lesbian and Gay Rights project.
Arkansas had barred gays from becoming foster parents, but a judge said the law was unconstitutional in December.
Under the Texas bill, anyone who applies to be a foster parent or a foster parent whose performance is being evaluated must say whether he or she is homosexual or bisexual. Anyone who answers yes would be barred from serving as a foster parent. If the person is already a foster parent, the child would be removed from the home.
Eva Thibaudeau, a social worker, said she and her partner of eight years have adopted four children and have served as foster parents to 75.
"I am just so hurt and surprised, especially now (when) we are facing an ongoing crisis of not having enough resources to take care of foster children," she said.
The bill follows recent child slayings that occurred after caseworkers investigated suspicions of neglect or abuse and decided the children were safe to remain with their parents.
It would give all of Child Protective Services' foster care and case management duties to private companies, which already manage 75 percent of foster homes in Texas.
The Senate sponsor of the bill, Jane Nelson, R-Lewisville, told the Fort Worth Star-Telegram Wednesday she had a lot of questions about Talton's amendment.
"My biggest question is how many kids would be displaced with this and where are we going to put them," she said.
The Star Telegram also reported that Randall Ellis, executive director of the Lesbian/Gay Rights Lobby of Texas, estimated that between 2,000 and 2,500 kids could be affected.
"The truth is that a parent's sexual orientation has no negative consequence on the children that are raised in those homes," he said at a news conference arranged by House Democrats opposed to the amendment. "Those children are not adversely affected."