According to Official Guinness Records,
Published on 1 August 2008 by Tokyo Shigesato Itoi Office K.K. (Japan), the audio book "50 Lectures" by Takaaki Yoshimoto (Japan) is 6,943 minutes (115 hours 43 minutes), making it the longest audio book. The audio book contains content from Mr Yoshimoto's lectures from the 1960's and 70's. Yoshimoto is a Japanese poet, literary critic, and philosopher from Tokyo. He is the father of the famous Japanese writer known as Banana Yoshimoto and of the cartoonist Haruno Yoiko.
For a complete list of 2008 records, please visit 2008 Guinness Records in Japan.