The purpose of this study was to examine the effect of a Learning Activity Package (LAP) incorporating Isan lullaby melodies on the development of basic brass instrument skills among music major students. The study involved two groups of participants: 5 expert scholars in music education and learning management, who evaluated the LAP, and 30 students enrolled in a Basic Brass course, who used the LAP during the semester. The main instruments were the Isan Lullaby -- music melody sung to send children to sleep in the northeastern Thailand, Learning Activity Package for basic brass skills, consisting of nine structured practice sets focused on various brass playing techniques on Isan lullaby melodies, a brass instrument skill rubric, and an LAP evaluation form. The students' performances were analyzed using mean scores, standard deviation, process/product effectiveness with 80/80 criteria, and paired samples t-test. The study found that the use of Isan lullabies in the LAP significantly improved the participants' brass instrument skills, as shown by their progress during practice sessions and post-test evaluations. The structured exercises helped students develop critical skills such as breath control, articulation, and musical expression. The result contributes to the growing body of evidence supporting the use of culturally relevant music, such as Isan lullabies, in Learning Activity Packages to effectively enhance music education and performance skills.