Mental health problems are common in college students and yield poor functional outcomes. Despite these emotional and functional difficulties, only a small percentage of students seek treatment due to barriers such as stigma and lack of resources. College students also prefer Web-based services to in-person services; thus, mobile health interventions may be a favored, viable, and accessible option. Ecological momentary interventions (EMIs) incorporate technology to administer interventions and are widely and effectively applied for heterogeneous psychological problems. Mindfulness-based interventions ameliorate psychological distress and promote psychological well-being in college students. Therefore, the current study examined the effectiveness and perceived utility of an EMI incorporating mindfulness-based messages. Participants were 161 undergraduate students (70.19% female; 80.75% white) randomized to either a mindfulness-based EMI or mood monitoring condition (i.e., ecological momentary assessment (EMA)) for 21 days (2812 daily surveys). Contrary to expectations, the EMA condition did not show different outcomes from the EMI condition. Higher engagement in the mindfulness activities was related to higher levels of positive affect, and participants who reported being more aware of emotions (i.e., thoughts, feelings, and behaviors) due to the messages reported lower emotion dysregulation. More emotional awareness due to the mindfulness messages was related to greater usage of messages and a higher likelihood of recommending skills to a friend, and those reporting increased usage of mindfulness messages were more likely to recommend mindfulness skills to a friend. Participants found the mindfulness messages useful and helpful on average. Implications for research and designing of EMIs are discussed.