The objective of this study was to analyze the influence of the year–season effect on semen production parameters in the fertile AI boars. The evaluation was especially focused on the morphologically abnormal spermatozoa (MAS) incidence. It was microscopically evaluated after making fresh semen smears and staining on microscopic slides. MAS incidence 19.46 % was lower at first half-year than at second half-year 25.00 %. Spermatozoa with distal protoplasmic droplet were furthest participated in total MAS incidence. Its rate was the highest at fourth quarter in comparison with annual period. We found that season has the negative effect on sperm morphology and significantly affects boar sperm quality and subsequently AI dose quality.