Mobile mammography units (MMUs) can enhance access to breast cancer screening by providing convenient, cost-effective service, particularly for uninsured and underinsured women. However, prior studies indicate that acceptability concerns about quality and privacy, among other issues, may prevent women from utilizing MMUs. The current study employs a within-participant experimental design exposing participants to messages about different MMU characteristics to determine which characteristics are most effective in persuading them to use an MMU. The study also examined how messaging interacts with participants' ethnic identity to influence outcomes. Data were collected from a diverse sample of uninsured and underinsured women as part of a formative study to promote the utilization of a mobile mammography facility in Central Texas. Results of mixed-effect linear models show that messages about equity, appointment convenience, privacy and comfort, and quality of equipment and staff were rated as more persuasive than messages about convenience of location and language accessibility. However, Hispanic women rated language accessibility higher than other participants did. The results can guide MMU organizers and promotion managers as they determine the best approach to promote mobile mammography services in different communities.