Penelitian ini bertujuan untuk mengetahui apakah ada peningkatan signifikan pada kemampuan siswa dalam menulis setelah siswa diajarkan menggunakan WhatsApp sebagai media dalam pembelajaran menulis. Penelitian ini adalah penelitian kuantitatif. Sampel penelitian ini adalah 30 siswa tingkat pertama SMAN 3 Bandar Lampung. Test menulis digunakan sebagai alat untuk pengambilan data. Hasil penelitian menunjukkan bahwa terdapat peningkatan signifikan pada kemampuan menulis siswa setelah penerapan WhatsApp dalam menulis teks deskriptif dan aspek content adalah aspek menulis yang paling meningkat. Dapat disarankan bahwa mengajarkan menulis teks deskriptif menggunakan WhatsApp efektif dalam meningkatkan kemampuan menulis siswa. The objectives of this research were to find out the increase of the students’ writing achievement after the students were taught by using WhatsApp as the media in teaching writing and to investigate which aspect of writing got the highest score after the implementation of WhatsApp in teaching writing descriptive text. This research was quantitative research. The subjects were 30 students of the first-grade students of SMAN 3 Bandar Lampung. The writing tests were used as the research instrument. The data were analyzed by using the Repeated Measure t-test. The result showed that there is a statistically significant increase in students’ writing achievement after the implementation of WhatsApp in teaching writing descriptive text and the content aspect of writing was the aspect that improved the most. This suggests that teaching writing descriptive text through WhatsApp is effective in increasing students’ writing achievement.Keywords: WhatsApp, teaching writing, descriptive text.