<![CDATA[This study aimed to identify students misconceptions regarding the law of conservation of mass and to examine the effectiveness of laboratory activities in reducing these misconceptions. The study employed a quantitative descriptive using a Pre-Experimental One Group Pretest-Posttest Design involving 33 students of class X-2 at SMAN 11 Surabaya. The study was conducted in one experimental class without a control group. The research instrument used was a three-tier diagnostic test consisting of the categories understanding, misconception, not understanding, and uncertainty. Data were collected through observation, documentation, pretest and posttest. Data analysis was conducted using the Shapiro-Wilk normality test, Wilcoxon signed-rank test, and N-gain calculation with the assistance of SPSS version 32. The results showed that the percentage of students experiencing misconceptions decreased from 82% in the pretest to 3% in the posttest, while the percentage of students in the understanding category increased from 15% to 97%. The Wilcoxon Signed-Rank Test showed a significance value of <0,001, indicating that H0 was rejected and H1 was accepted. In addition, the average N-gain score was 0,9294, which falls into the high category. These findings indicate that the implementation of a mass comparison laboratory activity was effective in reducing students misconceptions and improving their understanding of the law of conservation of mass through direct empirical learning experiences and conceptual reconstruction.]]>
