To analyse the effects of supplemental autologous seminal plasma on boar semen quality before freezing and after thawing, thirty ejaculates were collected from six Pietrain boars. The main factors of a 2 x 2 x 2 factorial arrangement of treatments were Beltsville thawing solution (BTS), seminal plasma before freezing, and seminal plasma after freezing-thawing. The percentage of acrosome-intact sperms was reduced by semen dilution. There were no interactions of main factors. The addition of seminal plasma to semen before freezing did not affect semen quality, but the addition of seminal plasma after freezing-thawing increased the percentage of acrosome-intact sperm. This approach indicates that the addition of seminal plasma to boar semen after freezing-thawing improves semen quality.