Inmates sentenced as juveniles who have served at least 15 years can petition a judge for resentencing under the new law.
A judge could then reduce the sentence to 25 years to life if the inmate shows remorse and is taking steps toward rehabilitation.
Democratic Senator Leland Yee authored the bill.
He says the state shouldn't lock kids up and throw away the key.
YEE: "Not a whole lot of evidence exists that these kinds of sentences really deters anybody from doing anything whatsoever, so I think we need to be a little bit more understanding, enlightened and really look to the future of our society."
Opponents say the law is unfair to victims' families.
Yee succeeding in getting the legislation passed only after
excluding juveniles who tortured their victims or killed a public
safety official.