Gov. Jerry Brown said Thursday he signed the bill, which makes California the first state in the country to require lessons about the contributions of people who are gay, lesbian, bisexual and transgender.
Gay history will become part of the social studies curriculum. The legislation doesn't specify the grade in which it will be taught.
The new law, SB48, requires schools to adopt textbooks and other teaching materials that cover the contributions and roles of sexual minorities, as soon as the 2013-2014 school year.
Supporters say the bill will teach students to be more accepting of gays and lesbians in light of the bullying that happens to gay students.
The bill has drawn criticism from some churches and conservative groups that argue such instruction would expose students to a subject that some parents find objectionable.
The Associated Press contributed to this report.