The former president, in a wheelchair and neckbrace, was smiling when he took to the field with his wife. He then threw the first pitch to the Astros' Jed Lowrie.
Bush has been sporting a neck brace since he fell at his home in July and broke a vertebra in his neck.
Barbara Bush said she thought the first pitch was "great."
"We're big Astros fans," she said, according to Bush spokesman Jim McGrath.
Today is Game 3 of the American League Division Series.
The Associated Press contributed to this report.