The purpose of the study was to examine the effect of using Six Thinking Hats (STH) strategy on the development of writing skill and creativity of seventh grade EFL students. A pretest and posttest quasi-experimental research design was employed involving 65 (34 control, 31 experimental) seventh grade EFL students studying in one of the higher secondary schools under Trongsa district. The writing ability test was administered for both the groups to determine the differences in their learning achievements. The writing skill of English for the experimental group was taught using STH strategy while the control was taught using a conventional method. A t-test for the pretest revealed that there was no significant mean difference between the two groups, indicating a homogenous learning ability at the beginning (p=0.78). However, the posttest analysis revealed a statistical significant difference between the mean scores of writing skills in favor of experimental group (M=15.17, SD=2.23) than the control group (M=11.89, SD=2.46) at p=0.00, indicating the improvement of students writing skill and creativity due to the treatment of STH strategy.