This study presents the synthesis, characterization, and biological evaluationof two novel quaternary ammonium compounds (QACs):Benzyltrimethylammonium chloride (QAC-1) andDodecyltrimethylammonium bromide (QAC-2), with a focus on theirpotential as cosmetic preservatives. QAC-1 and QAC-2 were synthesized viaalkylation reactions and characterized by FTIR spectroscopy, whichconfirmed the presence of key functional groups such as C–H stretching andN⁺–CH₃ vibrations. Theoretical and practical yields were calculated, withQAC-1 showing a significantly higher yield (78.08%) compared to QAC-2(39.99%). Antibacterial activity was assessed using the cup plate method,where QAC-1 exhibited a larger zone of inhibition (4.0 cm) than thestandard cetrimide (3.5 cm), while QAC-2 showed moderate activity (3.2cm). Compatibility studies with common cosmetic excipients revealed goodstability of both QACs with hydrophilic substances like glycerin andpropylene glycol, whereas lipophilic excipients such as stearic acid and cetylalcohol led to phase separation or precipitation. These findings highlightQAC-1 as a promising candidate for application as a novel cosmeticpreservative, particularly in water-based formulations. Further toxicologicaland formulation studies are recommended to explore their full potential.