The aims of this study were to measure the antioxidant enzyme activity of superoxide dismutase (SOD) and glutathione peroxidase (GPX1) in seminal plasma (SP), the influence of temperature overtime on such enzymes and, to assess post-thaw viability of semen supplemented with autologous or homologous SP by eosin-nigrosin (EN) and hypoosmotic tests (HOST). A total of 48 sperm-rich fractions from 8 boars were collected and equally divided for SP antioxidant activity determination or cryopreservation experiments. Marked differences in SP antioxidant activity were found amongst individuals. SOD values ranged from 7.88 ± 0.04 U/g to 12.01 ± 0.07 U/g. Restricted maximum likelihood variance components estimates (REML) indicated that 98% of the variation resided between individuals (p<0.05). In addition, GPX1 activity ranged from 0.03 ± 0.001 U/g to 0.05 ± 0.005 U/g with a REML between and within individual of 58% and 42%, respectively (p<0.05). Further, temperature largely influenced SOD and GPX1 activity (Spearman's ρ ≥ 0.77; main effect p<0.01). Regardless, sperm viability improved significantly in groups supplemented with 20% (v/v) SP compared with control as per EN 27 ± 0.59 % vs. 26 ± 0.23 % or HOST 28 ± 0.27 % vs. 18 ± 0.27 % (p<0.05). Although there was an additive effect of SP on sperm viability, the antioxidant levels were not strongly correlated to sperm morphology. Therefore, other factors in seminal plasma are contributing to sperm viability and overall fitness towards a successful fertilization.