With the emergence of programs that focus on socio-emotional regulation through online intervention, our focus is to move beyond the current literature to look at how personality might help to identify those in need of such an intervention, while also assessing if personality may moderate the overall efficacy of the treatment in middle-aged adults. In particular, our focus is on the established improvements that similar programs have shown to have on positive affect (PA), negative affect (NA), and emotional reactivity (ER). Through a randomized controlled trial, this research examines whether an online social intelligence training (SIT) program improves socio-emotional regulation compared to an attention-control (AC) condition. During the pre- and post-test phases of the study, participants (N = 230) completed a questionnaire, along with online surveys for 14-days that included measures of social connectedness, emotional awareness, and perspective-taking. Our analysis, while lacking significant findings in the way of PA and NA, shed light on how SIT programs can improve ER, while personality can simultaneously predict baseline levels of ER and moderate the efficacy of the program.