A disciplinary panel heard that Peter Carless, who taught at Cathays High School, took the girl to the Cotswolds as a Valentine's Day treat.
Mr Carless admitted he had been at the hotel on Valentine's Day in 2008, but said he was not with the girl pupil. He denied having an inappropriate relationship with the student, and spending a night in the hotel at Tewkesbury, Gloucestershire with her.
Presenting officer Martin Jones told the panel that the girl told police she and Peter Carless spent the night together in a hotel. She said they had not had a sexual relationship 'but there had been kissing involved.'
The hearing heard that Mr Carless confessed to another member of school staff after his relationship with the girl came to an end.
School IT technician Darren Ferguson told the hearing: "He said: 'I've got something serious to say and you might hate me for it'.
"He told me of some events which involved him having a relationship with a pupil.
"Peter told me he wanted to get back with this girl but she had said no.
"I told him he shouldn't because he would risk everything."
The hearing heard that they later rekindled their relationship and arranged to go to the four-star hotel on Valentine's Day.
The student was interviewed by police and admitted spending the night with her teacher, who was not charged in connection with the allegation.
Peter Williams, the disciplinary panel chairman, said the panel was satisfied Carless had entered into an inappropriate relationship with a female pupil and that his conduct 'fell short of that expected of a registered teacher and therefore amounts to unacceptable professional conduct.'