<p><i>Aerococcus viridans</i>, an emerging pathogen, is responsible for the recent increase in cases of bovine mastitis. However, its specific effects on mastitis remain largely unexplored. In this study, we examined the correlation between <i>A. viridans</i>-induced mastitis infections and somatic cell counts (SCCs), and characteristics of <i>A. viridans</i> isolates from bovine mastitis milk. Among 1774 mastitis milk samples collected between 2016 and 2021 in South Korea, 69 (3.9%) <i>A. viridans</i> isolates were obtained. Mastitis milk samples containing <i>A. viridans</i> exhibited significantly higher SCCs than did non-mastitis samples. Most isolates (80.5%) were associated with subclinical mastitis (200–1200 × 10³ cells/mL), whereas 19.5% were associated with clinical mastitis (&gt; 1.2 × 10⁶ cells/mL). In pulsed-field gel electrophoresis analysis, <i>A. viridans</i> isolates displayed substantial genetic diversity, with no dominant clones identified. Antimicrobial susceptibility testing revealed high resistance rates to ceftiofur (46.4%) and oxacillin + 2% NaCl (44.9%) among β-lactams, followed by tetracycline (36.2%) and erythromycin (10.1%), with 21.7% isolates being multidrug-resistant. Fifty-four isolates (78.3%) were able to form biofilms, with all recent isolates being biofilm-positive, in contrast to several earlier non-producers. Our findings suggest the necessity for targeted management strategies and continuous monitoring for mitigating <i>A. viridans</i>-induced mastitis in dairy cows.</p>