A woman while looking through her boyfriend's phone found a video of him having sex with her Staffordshire bull terrier.
Wayne Bryson, from Louth, Lincolnshire, was arrested after his girlfriend handed the phone to the police, Metro.co.uk reported.
The 19-year-old boy pleaded guilty to a charge of performing an act of sexual penetration with a dog when he appeared at Skegness Magistrates' Court.
According to Grimsby Telegraph, Bryson was also caught with 10 pounds worth of cannabis, which he said he had bought wet and was drying out.
The teenager was given bail on the understanding that he is not allowed to be alone with animals and will be will be sentenced on March 5.