Purpose: In recent years, proton magnetic resonance spectroscopy (MRS) has emerged as a non-invasive technique for measurement of fat content in the liver. The technique is often applied for overweight and obese patients. However, excessively obese patients cannot be examined in most conventional magnetic resonance systems due to limited space. The purpose of this study was to examine the ability of open 1T system to monitor liver fat with proton MRS and to compare hepatic fat fractions (HFFs) obtained using an open 1T system with assessment with 3T proton MRS. Methods: The study included 23 children and adolescents up to 20 years of age with a body mass index above the 97th percentile according to age and gender. Proton MRS for each patient was performed in both 1T and 3T using point resolved spectroscopy sequence in a single volume positioned in the right liver lobe. Results: Average T2 relaxation times obtained for an open 1T system (55 ± 7 ms for water and 85 ± 11 ms for fat) were higher than average T2 relaxation times obtained for a 3T system (31 ± 4 ms for water and 66 ± 10 ms for fat). HFFs measured using an open 1T system showed strong correlation with HFFs measured using a 3T system (r = 0.99, P < 0.0001). Conclusions: Proton MRS measurements of HFF with an open 1T system are feasible. Open 1T system may reliably replace 3T magnetic resonance system for the assessment of liver fat.