Key challenges in providing lifelong antiretroviral therapy (ART) to pregnant and breastfeeding women (Option B+) in sub-Saharan Africa include achieving long-term adherence and retention in care. One intervention that may help address these challenges is mobile text messaging. We evaluated the acceptability of a text messaging intervention to support women's ART adherence and retention in care in rural western Kenya. Forty in-depth interviews with 20 pregnant/postpartum women infected with HIV, their male partners, and four focus groups with 30 health care providers were conducted during September-November 2014. Data were coded and analyzed using thematic analysis. Findings revealed the following themes: (a) overall acceptability of the text messaging intervention; (b) proposed content of text messages; (c) format, timing, and language of text messages; and (d) potential challenges of the text messaging intervention. Findings were used to refine a text messaging intervention being evaluated at Kenyan study sites rolling out Option B+.