The pair, who both voice characters in Dr Seuss's The Lorax movie, made reference to rumours they are romantically involved through a cover of 'Pumped Up Kicks' by Foster the People.
Efron kicked off the twist in the song when he sang about people thinking he and 22-year-old Swift were "girlfriend and boyfriend".
Changing up the lyrics further, Swift and Efron suggested that coming on the television programme, hosted by Ellen DeGeneres was "weird" because of her quirky style of presenting.
Meanwhile, the Grammy Award winner made a joke of appearing on the show eight times and always being asked about who she is seeing.
Watch Taylor Swift and Zac Efron's performance below:
Earlier in the show, Swift told DeGeneres: 'We are not a couple. He's awesome, we are not a couple though. You hear people get together when they're shooting movies, co-stars."
The two were rumoured to be in a relationship after being spotted sharing a meal last month.
On January 6, the High School Musical star allegedly had a "flirty dinner with the country superstar" at an outdoor corner table at LA's Pace restaurant.
It was claimed that they "were deep in conversation and very giggly", after arriving together in Efron's Audi vehicle.
The Ellen DeGeneres Show airs in the UK on Really (Sky 248, Virgin 267, Freeview 20) weekdays at 4pm.
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