Russian President Vladimir Putin wants a heterosexual definition of marriage written into the constitution.
The proposals from Putin, who is now in his fourth term, would effectively ban same-sex marriage.
His proposed draft amendment to the constitution would also mention Russians' "faith in God" and proscribe giving away Russian territory to foreign powers.
The clause on territory threatens to escalate tensions with Ukraine over the Crimea, which Russia annexed in 2014.
Duma vice-speaker Pyotr Tolstoy spoke positively of the proposals on marriage in comments to reporters on Monday.
"For me, the most important proposal would fix the status of marriage as a union between a man and a woman," he said, according to the Guardian.
"And I am happy that this amendment has appeared under the signature of the head of state."
The proposals are to be voted on by the public. If the changes are approved, it will be the first time since 1993 that Russia has changed its constitution.
The country is officially secular but Putin is close to the Russian Orthodox Church.
He has also spoken out previously against gay marriage and attempts by some LGBT campaigners to replace 'mother' and 'father' with 'parent number 1' and 'parent number 2'.
"As far as 'parent number 1' and 'parent number 2' goes, I've already spoken publicly about this and I'll repeat it again: As long as I'm president this will not happen. There will be dad and mum," he said.