Fans have been clamouring to see a trailer for the movie, which will hit the big screen in December.
Jackson posted the video clip on his Facebook page, saying: "I think one or two of you asked to see this?"
Earlier, he had warned fans they would have to wait until October to see a full length trailer.
The video plays over a haunting backdrop of Pippin's Song and shows the dragon Smaug setting Lake-town on fire and legions of elves and orcs rushing into battle.
It was shown over the weekend to fans attending the Comic-Con convention in San Diego in the US.