The Objectives of this paper as an experimental research was to investigate the effect of Roundtable and Clustering teaching techniques and students' personal traits on students' achievement in descriptive writing. The students in grade ix of SMP Negeri 2 Pancurbatu 2016/2017 school academic year were chose as the population of this research. The research design was experimental research by using factorial design 2x2. The students were divided into two experimental groups. The experimental group was treated by using Roundtable teaching technique and control group was treated by using Clustering teaching technique. The students are classified into the introvert and extrovert personal traits by conducting the questionnaire and the students' achievement in descriptive writing was measured by using writing test, namely "Analytic Scoring" by Weigle. The data were analyzed by applying two-way analysis of variance (ANOVA) at the level of significance a = 0.05. The result reveals that (1) students' achievement in descriptive writing taught by using Roundtable teaching technique was higher than that taught by Clustering teaching technique, with Fobs = 4.59>Ftab=3.97, (2) students' achievement in descriptive writing with introvert personal trait was higher than that with extrovert personal traits with Fobs=4.90 > Ftable=3.97, (3) there is interaction between teaching techniques and personal traits on students' achievement in descriptive writing with Fobs =6,58 > Ftable=3.97. After computing the Tuckey-Test, the result showed that introvert students got higher achievement if they were taught by using Roundtable teaching technique while extrovert students got higher achievement if they were taught by using Clustering teaching technique.