This study was motivated by the still low student achievement in chemistry subjects, which is influenced by the lack of learning discipline. Learning discipline is an important factor in supporting students’ success in the learning process. The purpose of this study was to determine the effect of learning discipline on the learning achievement of Grade XI Cluster 4 students in chemistry at SMA Negeri 1 Siantar Narumonda in the 2025/2026 Academic Year. The method used in this research was a quantitative research method with inferential descriptive statistics. The population consisted of all Grade XI Cluster 4 students at SMA Negeri 1 Siantar Narumonda in the 2025/2026 Academic Year, totaling 36 students, and all of them were used as research respondents. Data were collected using a closed-ended questionnaire consisting of 30 items. The results of data analysis showed that there was a positive and significant effect of learning discipline on students’ achievement in chemistry subjects for Grade XI Cluster 4 at SMA Negeri 1 Siantar Narumonda in the 2025/2026 Academic Year, as evidenced by the following data analysis: 1) Analysis prerequisite tests: a) the normality test obtained an Asymp. Sig. (2-tailed) value of 0.200 > 0.05; b) the linearity test obtained a significance value for deviation from linearity of 0.974 > 0.05. 2) Hypothesis testing: a) the positive relationship test obtained an rxy value of 0.541 > rtable (α = 0.05, n = 36) = 0.329, indicating that there was a positive relationship between variable X and variable Y; b) the significant relationship test obtained a tcount value of 3.751 > ttable (α = 0.05, df = n-2 = 34) = 2.032, indicating that there was a significant relationship between variable X and variable Y. 3) Effect testing: a) the regression equation test obtained the regression equation Ŷ = 75.621 + 0.103X; b) hypothesis testing using the F-test obtained Fcount > Ftable (α = 0.05; numerator df = k = 1, denominator df = n-k = 36-1 = 35), namely 14.068 > 4.12. 4) The coefficient of determination test (r²) showed a result of 29.3%, while the remaining percentage was influenced by other factors. Therefore, H0 was rejected and Ha was accepted, meaning that there was a positive and significant effect of learning discipline on the learning achievement of Grade XI Cluster 4 students in chemistry at SMA Negeri 1 Siantar Narumonda in the 2025/2026 Academic Year.