Objectives <p>To evaluate the physicochemical, optical, and antimicrobial properties of a conventional glass ionomer cement (GIC) modified with anacardic acid (LDT11).</p> Materials and methods <p>LDT11, extracted from cashew nutshells, was incorporated into GIC (FX ULTRA, Shofu, USA) at 0.5%, 1%, and 2% (w/w), with 0% as control.&#xa0;Disc-shaped specimens (6–15&#xa0;mm diameter × 1&#xa0;mm thickness) were prepared for all evaluations<i>.</i> Setting time (ISO 9917; n = 3), acid-base reaction efficiency (FTIR, COO⁻/COOH ratio; n = 3), water sorption and solubility (ISO 4049; n = 5), diffusion coefficient (n = 5), surface roughness (Ra, Rz, Rv; n = 5), and color parameters (CIELab, CIEDE2000; n = 5) were measured. Antimicrobial characterizations were carried out, with discs inoculated with <i>Streptococcus mutans</i> UA159 and incubated anaerobically for 7 days (early biofilms) and 14 days (mature biofilms). Biofilms were dyed with the Live/Dead biofilm viability kit and then imaged using confocal laser scanning microscopy (n = 6). Data were analyzed using one-way ANOVA with Tukey post hoc or Kruskal-Wallis with Dwass-Steel-Critchlow-Fligner tests (p &lt; 0.05).</p> Results <p>LDT11 incorporation did not significantly affect setting time, acid-base reaction efficiency, solubility, diffusion coefficient, and surface roughness. FTIR spectra revealed no alterations in setting-related functional groups, while LDT11 was identified in the 1000–1100&#xa0;cm⁻¹ range. At 2%, LDT11 significantly increased water sorption and caused visible color changes (<i>p</i> &lt; 0.05). The 0.5% and 1% groups significantly reduced <i>S. mutans</i> viability compared to control, with the 1% group exhibiting the most pronounced and sustained effect (<i>p</i> &lt; 0.0001).</p> Conclusions <p>Incorporation of the anacardic acid derivative up to 1% maintained physicochemical properties of GIC while providing antimicrobial activity.</p>