Aim: Hyperemesis gravidarum (HEG) is characterized by severe and persistent nausea vomiting. The factors involved in the etiology of HEG aren’t known exactly. Heme oxygenase (HO) is a stress protein whose synthesis increases with oxidative stress and is highly expressed from placenta. Also, malondialdehyde (MDA) and nitric oxide (NO) levels are measured as oxidative stress marker in many studies. There is increasing evidence that oxidative stress may play a role in the pathophysiology of HEG in literatüre. In our study, we aimed to investigate HO-1 levels and oxidative stress status in serum of HEG patients. Material and Method: The study included 25 HEG patients and 25 healthy pregnant women without any signs and symptoms of HEG and matched for age, gestational age and body mass index were defined as control group. Serum HO-1 and NO levels were measured with enzyme linked immunosorbent assay (ELISA). Serum MDA levels were measured with spectrofotometric method. Results: No significant difference was determined between the groups in terms of age, gestational age and body mass index (p>0.05). In the HEG group, median (minimum-maximum) serum HO-1, NO and MDA levels were 3.03 (2.27–3.89) ng/mL, 5.25 (2.75– 18.75) micromol/ml and 21.82 (17.95–29.59) micromol/mL compared to 2.74 (0.24–3.06) ng/mL, 5.75 (1.75–9.75) micromol/mL and 16.41 (10.41–26.86) micromol/mL in the healthy individuals. Serum HO-1, NO and MDA levels were higher in the HEG group compared to the control group but therewere significant differences between HEG and control groups in terms of serum HO-1 and MDA levels (p=0.007 and p=0.004). Furthermore, when the patient and control groups were analyzed together, a significant, positive correlation was determined between serum HO-1 and MDA levels (r=0.38, p=0.014). Conclusion: Serum HO-1, NO and MDA concentrations increase in HEG, so we thought that there was a relation between oxidative stress and HEG.