Previous research supports a positive relationship between cognition and emotional stability, although findings regarding healthy older adults are inconsistent. Additionally, little is known about the mechanisms that underlie this association. Thus, the present study investigated the mediating effect of cognitive complaints on the bidirectional longitudinal association between cognition and emotional stability in old age. The study sample consisted of 500 older individuals (M age 62.97 years, SD 0.91, range 60–64 years; 52% male) from the Interdisciplinary Longitudinal Study on Adult Development. The results showed that cognitive complaints mediated the effect of cognition on emotional stability over 12 years even when taking baseline emotional stability, baseline cognitive complaints, depressive affect, gender, sensory functioning, and objective and subjective health into account. However, cognitive complaints did not mediate the effect of emotional stability on cognition. The results of the current study emphasize the importance of investigating cognition as a predictor of personality traits, and indicate that cognitive resources may serve as a protective factor for emotional stability in old age.