In learning English, students at the second year of SMP Muhammadiyah 1 faced difficulties to express and develop their ideas in writing. It happened because they were lack of vocabulary, so they cannot write the sentences in good pattern and cannot organize their writing well. So that the researcher wants to conduct a research entitled “The Implementation of Freewriting Technique in Improving Students’ Writing Ability”. The objective of this research was to know whether the implementation of freewriting technique can improve students’ ability in writing or not. The method of this research was an experimental quantitative research. The research used one group pre-test and post-test. The sample of this research was the second year students of SMP Muhammadiyah 1 that selected by using random sampling. Then the researcher employed some statistical formulas which were mean score, standard deviation, and T-score. After calculating the data, this research showed that the value of T-score was 11.26 (significant 0.05) with (df) 14 was 1.76. So T-score (11.26) was higher than T-table (1.76), therefore, the alternative hypothesis (Ha) was accepted and the null hypothesis (Ho) was rejected. It means the implementation of freewriting technique can improve students’ writing ability especially in writing friendly letter (short functional text).