Persalinan merupakan serangkaian proses yang berakhir dengan keluarnya bayi, dan selalu disertai dengan rasa nyeri, sehingga diperlukan metode nonfarmakologis untuk membantu mengurangi nyeri yang dialami ibu. Penelitian ini bertujuan untuk mengetahui efektivitas teknik relaksasi nafas dalam terhadap penurunan nyeri persalinan kala I fase aktif di UPT Puskesmas Kedabu Rapat Kabupaten Kepulauan Meranti. Jenis penelitian ini adalah kuantitatif dengan desain quasi experiment. Penelitian dilaksanakan pada bulan Agustus–September 2025. Populasi dalam penelitian ini adalah seluruh ibu bersalin sebanyak 80 orang dengan jumlah sampel sebanyak 22 orang ibu. Instrumen penelitian menggunakan lembar observasi Numeric Rating Scale (NRS). Analisis data dilakukan secara univariat dan bivariat menggunakan uji Wilcoxon. Hasil penelitian menunjukkan mayoritas responden sebelum diberikan relaksasi nafas dalam mengalami nyeri sedang sebanyak 18 orang (81,8%) dan sesudah diberikan relaksasi nafas dalam mengalami nyeri ringan sebanyak 20 responden (90,9%). Rata-rata intensitas nyeri sebelum yaitu 4,64 dan sesudah 2,23. Terdapat efektivitas relaksasi nafas dalam terhadap penurunan nyeri persalinan kala I fase aktif (p=0,000). Disarankan agar teknik ini lebih dipraktikkan dan diajarkan kepada ibu bersalin sebagai inovasi dan alternatif pilihan pengobatan. ABSTRACT Labor is a series of events that culminates in the delivery of the baby, and is always accompanied by pain; therefore, non-pharmacological methods are needed to help reduce the pain experienced by mothers. This study aims to determine the effect of the deep breathing relaxation technique on reducing pain during the active phase of the first stage of labor at UPT Puskesmas Kedabu Rapat, Meranti Islands Regency. This research is a quantitative study with a quasi-experimental design conducted from August to September 2025. The population consisted of all mothers who gave birth, totaling 80, with a sample size of 22 mothers. The research instrument used was an observation sheet based on the Numeric Rating Scale (NRS). Data analysis was performed using univariate and bivariate analysis with the Wilcoxon test. The results showed that before the intervention, most respondents experienced moderate pain (18 mothers, 81.8%), and after the intervention, the majority experienced mild pain (20 mothers, 90.9%). The average pain intensity before the intervention was 4.64 and decreased to 2.23 afterward. There was a significant effect of the deep breathing relaxation technique on reducing labor pain (p = 0.000). It is recommended that this technique be further implemented and taught to mothers as an innovation and alternative treatment option.