: In light of the escalating global concern over antibiotic resistance, this study aimed to evaluate the antimicrobial activity of the hydroalcoholic extract of Allium atroviolaceum and compare it with 0.2% chlorhexidine using the well diffusion, minimum inhibitory concentration (MIC), and minimum bactericidal concentration (MBC) methods against Streptococcus mitis (ATCC 6249), Streptococcus mutans (PTCC 16836), Streptococcus sanguinis (PTCC 1449), and Streptococcus salivarius (PTCC 1448). The well diffusion method revealed the inhibitory effect of the extract, with the highest activity observed against Streptococcus salivarius. Subsequently, MIC and MBC values were determined, indicating that the hydroalcoholic extract had MIC and MBC values of 3.12 mg/mL against Streptococcus sanguinis and 6.25 mg/mL against other strains (Streptococcus mitis, Streptococcus mutans, Streptococcus sanguinis, and Streptococcus salivarius). Chlorhexidine exhibited significantly lower MIC and MBC values of 0.0003%. Based on literature reviews, Allium species exhibit antimicrobial properties. The findings highlight the potential of Allium atroviolaceum extract as an alternative or complementary antimicrobial agent and warrant further investigation to identify its bioactive components and explore their mechanisms of action. This study contributes to understanding natural antimicrobial agents and their potential applications against bacterial infections.