Background: Poor quality of sleep is a common problem among female nurses due to the nature of nursing work. This situation may impact negatively on their physical and mental health and on their overall work performance. Purpose: This study was designed to explore the effect on the sleep quality of female nurses of sniffing essential lavender oil (lavender aromatherapy). Methods: This quasi‐experimental study was conducted at a regional hospital in southern Taiwan. A total of 100 qualified participants were randomly assigned to either the experimental group or the control group. The experimental group received lavender‐based aromatherapy for eight weeks (n=48) and the control group received no intervention (n=47). The main outcome indexes used the Pittsburgh Sleep Quality Index (PSQI) and heart rate variability (HRV). Results: After eight weeks of the Lavender‐Based Aromatherapy intervention, the differences between the PSQI pretest and posttest scores were statistically significant (p=.005) for the experimental group and not statistically significant (p = .052) for the control group. Furthermore, the control group registered significant pretest/posttest differences in terms of blood pressure, hear rate, heart rate variability (HRV), high frequency (HF), low frequency (LF), and LF/HF (p ＜ .001). The lavender‐based aromatherapy intervention effectively improved the sleep quality of experimental‐group participants. The present study demonstrated that lavender inhalation may have a persistent and short‐term effect on HRV with an increase in parasympathetic modulation that results in improved sleep quality in female nurses. Conclusions / Implications for Practice: The present study supports the efficacy of lavender‐based aromatherapy, a safe and convenient intervention, in improving the sleep quality of nurses. Improving the sleep quality of professional nurses is a priority issue due to their variable shift‐work schedules and critical role in ensuring the delivery of effective, high‐quality public healthcare.