Background <p>Impairments in mentalizing, the capacity for understanding mental states, are central to borderline personality disorder (BPD). This study examined a brief mentalizing intervention aiming to enhance the capacity and motivation for mentalizing in BPD.</p> Methods <p>Forty-eight adults with BPD (Sex: 81% female; Gender: 75% female) were randomized to a brief, single-session mentalizing or a control intervention. The mentalizing intervention involved prompts and practice in considering mental states underlying behaviors in interpersonal situations, while the control group involved an emotional sharing intervention. An observer-rated measure of mentalizing ability and a self-report measure of motivation for mentalizing were administered before and after the intervention. Self-report measures of subjective distress and the acceptability of the intervention were collected following the intervention.</p> Results <p>A significant improvement in mentalizing abilities was observed following mentalizing-enhancement (<i>d</i> = 0.69, <i>p</i> = .002), but not emotional sharing (<i>d</i> = -0.07, <i>p</i> = .64). Participants in the mentalizing-enhancement group reported significantly lower post-intervention distress than the emotional sharing group (<i>d</i> = 0.64, <i>p</i> = .03). Unexpectedly, the motivation for mentalizing decreased in both groups (mentalizing-enhancement/emotional sharing: <i>d</i> = -1.62/-1.16, respectively, <i>p</i>s &lt; 0.001).</p> Discussion <p>Brief and focused mentalizing interventions may enhance mentalizing and reduce distress in BPD and could be utilized for tailoring interventions for specific BPD deficits.</p>