The attack on Melania Geymonat, 28, and her girlfriend Chris, happened on the top of a double-decker London night bus as they were travelling to Camden Town in the early hours of May 30.
A group of young men began harassing them when they discovered they were a couple, asking them to kiss while making sexual gestures.
Miss Geymonat posted on her Facebook page: “In an attempt to calm things down, I started making jokes. I thought this might make them go away. Chris even pretended she was sick, but they kept on harassing us, throwing us coins and becoming more enthusiastic about it.
“The next thing I know is that Chris is in the middle of the bus fighting with them. On an impulse, I went over there only to find her face bleeding and three of them beating her up.
“The next thing I know is I’m being punched. I got dizzy at the sight of my blood and fell back. I don’t remember whether or not I lost consciousness. Suddenly the bus had stopped, the police were there and I was bleeding all over.”
Miss Geymonat added that the gang of at least four may have broken her nose during the ordeal, and stole a phone and bag from them before taking off into the night.
London Mayor Sadiq Khan described the attack as disgusting and misogynistic.
He said hate crimes against the LGBT+ community would not be tolerated in London.
Siwan Hayward, from director of compliance and policing at TfL, said: “This sickening attack is utterly unacceptable. Homophobic behaviour and abuse is a hate crime and won’t be tolerated on our network.
“All of our customers have the right to travel without fear of verbal or physical assault and we are working with the police to stamp out this behaviour on our transport network.
“We will do all we can to support the police investigation of this incident.”
Both women were taken to hospital for treatment to facial injuries.
Miss Geymonat said one of the men spoke Spanish and the others had British accents.
Scotland Yard has issued an appeal for witnesses to come forward.