Drama teacher Artyom Nazarov was one of thousands of Russians arrested at Saturday's (January 23) protests in support of jailed opposition politician Alexei Navalny.
He was still in custody some 40 hours later when he found out his college was firing him.
The rector of Moscow's Institute of Theatrical art publicly supports President Vladimir Putin.
And wrote on its website that Nazarov had deliberately committed a crime by protesting, and that was an "amoral act".
Nazarov says he knew he'd be sacked, and stands by his choice.
"I was expecting it from the moment police caught me on the road and started to carry me. So yes, I expected it. I did not expect that kind of wording, which insults me deeply. I think it would have been amoral of me not to be there. It would have been amoral to demand that my students don't express their opinion. Or have an opinion. That is amoral."
His firing illustrates the risks the demonstrators run. Police had declared the protests illegal, and rounded up more than 4,000 people, a monitoring group said.
Nazarov says he wasn't even planning to protest, but his son told him he was going, and he felt he couldn't stay on the sidelines.
"I haven't liked the direction our country is going in for a long time. I wish Russia was a European nation, and a country I wasn't ashamed of... And as time goes by, there are more and more reasons to be ashamed. And it pains me deeply."
Another protest is planned for Sunday. Nazarov says he doesn't know if he'll go yet, but he isn't afraid.
What frightens him more, he says, is living in a country that is, quote, descending into "an abyss of absurdity and fear".