In the United States, 90 million adults have low health literacy. An important public health challenge is developing obesity treatment interventions suitable for those with low health literacy. The objective of this study was to examine differences in sociodemographic and clinical characteristics as well as weight and intervention engagement outcomes by health literacy. We randomized 194 participants to usual care or to the Shape Program intervention, a 12-month digital health treatment aimed at preventing weight gain among overweight and Class I obese Black women in primary care practice. We administered the Newest Vital Sign instrument to assess health literacy. More than half (55%) of participants had low health literacy, which was more common among those with fewer years of education and lower income. There was no effect of health literacy on 12-month weight change or on intervention engagement outcomes (completion of coaching calls and interactive voice response self-monitoring calls). Low health literacy did not preclude successful weight gain prevention in the Shape Program intervention. Goal-focused behavior change approaches like that used in Shape may be particularly helpful for treating and engaging populations with low health literacy.