This study was carried out on 10 stress-negative Pietrain boars including 3 pigs of halothane genotype CC and 7 of CT at the pig breeding farm of Hanoi University of Agriculture in order to evaluate effects of season (Spring, Summer and Autumn) and halothane genotype (CC and CT) on the production performance and semen traits. The results showed that the difference in daily average gain was not significant between CC (559.57 g/day) and CT boars (546.31 g/day). The halothane genotype did not affect semen traits (P0.05) except ejaculation volume (P0.001). Ejaculation volume of CC genotype (270.95ml) was higher than that of CT (220.82ml). Season had significant effect on ejaculation volume, sperm concentration and pH of semen (P0.OO1) as well as total number of sperms moving straight ahead per each ejaculation (P0.05). Semen volume was highest in Autumn (293.02 ml) followed by Summer (195.00 ml) and Spring (190.86 ml) while this tendency was inverse for sperm concentration. Total number of sperms moving straight ahead per each ejaculation was highest in Autumn (47.15 billion) followed by spring (45.20 billion) and lowest in Summer (36.74 billion). Semen traits of the stress-negative Pietrain boars were in accordance to the standards of technical criteria for animal breeding accoprding to the Decision No.1712/QD-BNN-CN (Ministry of Agriculture and Rural development, Vietnam), except sperm motility and growth performance were lower than specified.