Collaborative Online International Learning (COIL) is a simulated global exchange experience that utilizes technology to bridge the gap between classrooms worldwide. Past research suggests that COIL may be useful in facilitating intercultural communication effectiveness and cultural humility for adult learners. As such, this quantitative study sought to examine the effects of a COIL experience that connected adult learners in the United States and Brazil on their intercultural effectiveness and cultural humility. Two instruments were used to collect data, including the Cultural Humility Scale and Intercultural Effectiveness Scale before and after the COIL experience. Data analyses revealed statistically significant increases in participants' intercultural effectiveness and cultural humility following the COIL experience. These findings provided insights into the effects of COIL on the intercultural effectiveness and cultural humility of adult learners. They also informed andragogical practices for cultivating attitudes, skills, and behaviors for intercultural interactions among adult learners in educational and other professional settings. However, further research on the outcomes of COIL is beneficial.