The Effect of Constructivism Learning Through Random Sentences Forming to the Ability to Write Deductive Paragraph of Students Grade XI SMA Negeri 1 Denpasar. This research has purposed to analyze and describe the ability to write deductive paragraph through implementation of constructivism learning by random sentences forming method and the effect of conventional learning through of writing learning through constructivism learning by random sentences forming method to the ability to write deductive paragraph students grade XI SMA Negeri 1 Denpasar. Subject population in this subject are all students grade XI – Science SMA Negeri I Denpasar which spread in eight classes. Sampling done by random class technique gradually. From eight classes, two classes were chosen as sample. From these two classes were chosen randomly as experiment group and control group. This research uses experimental plan with the post test only control group design. The data was analyzed by one way variant analysis. The result of the research shows that: (1) the ability to write deductive paragraph by students who attend writing lesson with constructivism learning with random sentences forming method in qualification is very good with average 82,956, (2) the ability to write deductive paragraph by students who attend writing lesson by conventional learning in qualification is good with average 68,217, and (3) there are significant effects of writing ability of deductive through constructivism learning by random sentences forming method to the ability to write deductive paragraph in students grade XI SMA Negeri 1 Denpasar.