Purpose <p>To evaluate the sedative effects of low-concentration nitrous oxide (LCNO) anesthesia during cataract microsurgery (CMs) using bispectral index (BIS) monitoring.</p> Methods <p>Thirty patients undergoing sequential CMs were randomized into the following three groups: Group A (LCNO for the first eye, oxygen for the second), Group B (oxygen for the first eye, LCNO for the second), and Group C (oxygen for both eyes) (<i>n</i> = 10 per group). BIS values, blood pressure, heart rate, and oxygen saturation were recorded at four time points: upon entering the operating room (T1), at the start of surgery (T2), at the conclusion of surgery (T3), and upon exiting the room (T4). A linear mixed model analysis was performed, with participants as the variable factor and group (LCNO-first, O₂ first, both O₂), duration (first and second eye), time (T1, T2, T3, and T4), interaction terms, and the initial values of each parameter (at entry) as fixed factors.</p> Results <p>BIS values at T2 and T3 were significantly lower in groups under LCNO compared to those under oxygen-only conditions (<i>p</i> &lt; 0.001). No significant changes in heart rate, blood pressure, and oxygen saturation were observed in both groups.</p> Conclusion <p>LCNO provided mild sedation during CMs, enhancing patient comfort without causing adverse effects.</p>