Maternal substance abuse is a risk factor for child maltreatment, child attachment insecurity, and maladaptive social information processing. The aim of this study was to conduct a quantitative exploratory evaluation of the effectiveness of an attachment‐based parent program, Circle of Security‐Parenting (COS‐P; G. Cooper, K. Hoffman, & B. Powell, 2009), with a community sample of 15 mothers in residential treatment for substance abuse. Participants attended nine weekly group sessions and were given three measures at pretest and posttest: the Emotion Regulation Questionnaire (J.J. Gross & O.P. John, 2003), the Parent Attribution Test (D. Bugental, ), and the Parenting Scale (D.S. Arnold, S.G. O'Leary, L.S. Wolff, & M.M. Acker, 1993). The results indicate that mothers who attended the majority of group sessions showed greater improvements on all three variables. Participants who attended some of the sessions showed some improvements on the measures, but participants who did not attend the group sessions had no improvements, and on some measures, declined significantly. Further analyses of demographic data indicates that participants with more education, no personal history of child maltreatment, less time in the residential program, and lower social desirability scores demonstrated more positive outcomes. These findings suggest that the COS‐P may positively impact parental risk factors associated with child maltreatment and maladaptive social information processing in the context of residential substance‐abuse treatment.