Fixed and growth mindsets describe the underlying beliefs people have about human capacity to grow (Dweck, 2006). The theoretical framework of growth mindset classroom cultures (Murphy et al., 2021) as interpreted in the context of music education provided a solid foundation. This qualitative multiple case study explored the mindset construct and its role in first-year music teachers from the United States and China. Three research questions were focused on their mindset development about their own teaching ability and students' learning ability throughout their first year of teaching and any similarities and differences in their mindsets across two cultures. Through within-case and cross-case analyses of their experiences via interview and teaching material, six novice music teachers' mindsets displayed differing results and varied after teaching practice. Three music teachers changed their mindsets and moved toward the growth end of the mindset spectrum in terms of their teaching ability, and there was no change in six music teachers' mindsets toward students' learning ability at the end of their first year of teaching. All six participants' perspectives on the main themes of the COVID-19 pandemic, motivation, and musical talent further revealed mindset differences in terms of different cultures. The findings suggest that music educators should gain a thorough understanding of the growth mindset and apply this concept to their teaching. To achieve this goal, it was recommended that teacher preparation programs in music teaching and learning establish a growth mindset culture as part of instruction. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]