Introduction. Partner behaviors and attitudes can motivate and encourage, or conversely undermine, a tobacco user’s cessation efforts. Previous partner support interventions for tobacco cessation have largely focused on positive and negative behaviors. We developed a theoretically based intervention (UCare) for women who wanted their male partner to quit smokeless tobacco, based on perceived partner responsiveness--the finding that support is best received when the supporter conveys respect, understanding, and caring.Methods. We recruited 1,145 women and randomized them to receive either immediate access to the UCare website and printed booklet (Intervention), or to a Delayed Treatment control. We assessed supportive behaviors and attitudes at baseline and six-week follow-up, and the ST-using partner's abstinence at six weeks and 7.5 months (surrogate report).Results. For partners of women assigned to Intervention, 7.0% had quit all tobacco at 7.5 months, compared with 6.6% for control (n.s.). For partners of women completing the intervention, 12.4% had quit all tobacco at 7.5 months, compared with 6.6% for Delayed Treatment (p<.01). Change in responsiveness-based behaviors and instrumental behaviors at six weeks mediated 7.5-month cessation, and change in responsiveness-based attitudes mediated the change in responsiveness-based behaviors, indirectly increasing cessation.Conclusions. A responsiveness-based intervention with female partners of male smokeless tobacco users improved supportive attitudes and behaviors, leading to higher cessation rates among tobacco users not actively seeking to quit. The study demonstrates the potential for responsiveness as a basis for effective intervention with supporters, and this approach may reach tobacco users who would not directly seek help.