Background <p>Dyslipidemia is associated with cognitive impairment, but the exact link between them remains controversial. The non-high-density lipoprotein cholesterol to high-density lipoprotein cholesterol ratio (NHHR) is an emerging plasma marker for comprehensively assessing lipid metabolism, and its association with cognitive impairment has not yet been elucidated.</p> Objective <p>This investigation intends to delineate the association between NHHR and cognitive impairment.</p> Methods <p>A cross-sectional analysis was performed utilizing data from the baseline survey of China Health and Retirement Longitudinal Study (CHARLS 2011–2012). Logistic regression and restricted cubic spline regression (RCS) analyses were conducted to explore the relationship between NHHR and cognitive impairment. Stratification and interaction testing were applied to assess the stability of our findings. Mediation analysis was employed to evaluate whether body mass index (BMI) mediated the association between NHHR and cognitive impairment.</p> Results <p>In the Model 3, the odds of cognitive impairment were significantly lower in the three higher NHHR quartiles compared to the lowest quartile (P for trend &lt; 0.001). Further analysis revealed an L-shaped association between NHHR and cognitive impairment, with a cutoff value of 3.030. The negative association was stable across different subgroups. Mediation analysis indicated that BMI was a significant mediator, accounting for 32.1% of the total association.</p> Conclusions <p>NHHR exhibits a negative association with cognitive impairment within a certain range, forming an L-shaped relationship. Moreover, this association is partially mediated by BMI. NHHR can serve as a significant associated factor for cognitive impairment.</p>