The aim of this study was to investigate whether there is a relationship of young boar testes size with semen traits and with productive traits. The dimensions (length, width and volume) of each testis and semen traits (semen volume, percentage of sperm with progressive motility, sperm concentration, total number of sperm in semen, percentage of sperm with normal acrosome, percentage of sperm with major and minor morphological defects, osmotic resistance test value and activity of aspartate aminotransferase in seminal plasma) were determined on 120 young boars aged 6 months. At 180 day of age, the boars backfat thickness and leanness (by ultrasonic apparatus) and body weight were also measured. The average daily gain was determined in the period from 70 to 180 days of age of the boars. The results showed that the sperm concentration, total number of sperm in semen and percentage of progressive motile sperm were a significantly positively correlated with width and volume of the left (p ≤ 0.01) and right testis (p ≤ 0.05) and with total volume of both testes (p ≤ 0.01). But the highest values of correlation coefficients were found between the width of the left testis and sperm concentration, total number of sperm in semen and percentage of progressive motile sperm. A correlations of dimensions (length and width) and volume of testes with other semen traits were very low and statistically non-significant. The volume of testes (left and right testis and total testes) was significantly positively correlated with body weight at 180 days of age and daily gain (p ≤ 0.01), but lower correlation coefficient was between left testis and daily gain (p ≤ 0.05), whereas correlations were low and non-significant with leanness and backfat thickness.