South Korea recently revised its livestock regulations to enforce mandatory group housing for pregnant sows beyond six gestation weeks until 2030. However, group housing of pregnant sows can influence their social hierarchy and feed competition, thereby affecting their reproductive performance and welfare. Although governing regulations of minimum space requirements for group-housed pregnant sows have not yet been established in South Korea, a minimum space of 1.9 m² per sow is estimated to be necessary. Therefore, this study investigated the effects of space allowance (SA; 1.9 m², 2.3 m²) during pregnancy and social training (ST; -, +) during the growing period on the productivity and welfare of primiparous sows. Thirty-six gilts were divided into four groups based on space allowance during gestation and social training during the growing period: 1) SA 1.9 m², non-ST (-), 2) SA 1.9 m², ST (+), 3) SA 2.3 m², non-ST (-), and 4) SA 2.3 m², ST (+). Measurements were basic performance, reproductive performance, colostrum composition, lameness score, and number of skin lesions of primiparous sows. The sow group in SA 1.9 m² had higher (p < 0.05) body weight during farrowing crate relocation, litter weight of total litter, stillbirth, and alive born, and number of skin lesions during the overall period of group housing than that in SA 2.3 m². However, there were no effects of SA on colostrum composition and lameness score of sows. The sow group with ST had higher (p < 0.10) litter size of total born and alive born and fewer (p < 0.05) number of skin lesions during the overall period of group housing than that without ST. However, no effects of ST were found on sow performance, colostrum composition, and lameness score. In addition, there were no interaction effects between SA and ST on all measurements in this study. In conclusion, primiparous sow aggression may be reduced by increasing space allowance during gestation with social training during the growing period.