This research intends to find out the effectiveness of the show don’t tell technique to teach writing descriptive text for the tenth-grade students of a senior high school in Demak in the academic year of 2020/2021. This study used a nonequivalent (pretest and posttest) control-group design. The population in this research is the tenth-grade students of a senior high school in Demak in the academic year of 2020/2021 that consist of class X A as experimental group and class X B as control group. The data collection techniques were pretest and posttest. The data analysis techniques were normality test, homogeneity test and t-test. The result of this research is that the show don’t tell technique is effective to teach writing descriptive text for experimental group. The effectiveness was proven by the result of t_score=3,243 that is higher than t_table=1,67. Since t_score>t_table, it means that there is a significant difference between the control group and the experimental group. Then, it implies that the show don’t tell technique can be used in teaching writing and also can be used by combining other additional methods.