Kanker payudara merupakan jenis kanker yang umum terjadi wanita. umumnya pasien yang menjalani kemoterapi mengalami gejala akibat proses penyakit atau efek samping pengobatan seperti nausea dan vomiting. Tujuan penelitian ini adalah untuk menjelaskan pengaruh aromaterapi lavender terhadap nausea dan vomiting pada pasien kanker payudara yang menjalani kemoterapi. Metode: penelitian ini adalah penelitian true experimental dengan desain randomized pre-post test with control group. Sampel penelitian melibatkan pasien kanker payudara yang menjalani kemoterapi one day care di RSUD dr. Soetomo Surabaya. Sampel dibagi menjadi 2 kelompok, kelompok aromaterapi (n = 20) dan kelompok kontrol (n = 20).  Aromaterapi lavender dilakukan mandiri oleh pasien dirumah setiap dua kali sehari selama tiga minggu berturut-turut (21 hari). Instrumen mengukur nausea dan vomiting menggunakan Rhodes Index Nausea, Vomiting and Retching. Data dianalisis menggunakan uji pair t test dan independent t test. Hasil: Skor nyeri pre kelompok aromaterapi 17.60 ± 3,05 dan post 8,40 ± 4,74 (p value <0,001). Independent t test menunjukkan nilai p value 0,001 (< 0,05). Kesimpulan: studi ini menunjukkan aromaterapi lavender inhalasi yang diterapkan secara berkesinambungan selama tiga minggu berturut-turut mampu menurunkan nausea dan vomiting pasien kanker payudara yang menjalani kemoterap Background: Breast cancer is the most common type of cancer suffered by women. Cancer patients generally experience side effects of chemotherapy such as nausea and vomiting. Aim : The purpose of this study was to determine the effect of aromatherapy on nausea and vomiting of breast cancer patients undergoing chemotherapy. Method: this study is a true experimental study with a randomized pre-post-test design with a control group. The study sample was breast cancer patients with one day care chemotherapy at RSUD dr. Soetomo Surabaya. The sample was divided into 2 groups, the aromatherapy group (n = 20) and the control group (n = 20) collected consecutively in August to September 2019. Inhalation lavender aromatherapy is performed independently by patients at home every 2 times a day for 3 consecutive weeks (21 days). The instrument measures nausea and vomiting using the Rhodes Index Nausea, Vomiting and restcing. data analysis using paired t test. Results: The aromatherapy group had a mean difference of pre-post test -9.20, higher than the control group 0.30. Paired t test showed that there were significant differences in mean pre and post test in the aromatherapy group with p value <0.001 compared to the control group p 0.741 (> 0.05). Conclusion: lavender aromatherapy inhaled continuously for three consecutive weeks can reduce the nausea and vomiting of breast cancer patients undergoing chemotherapy