Hemolysis, elevated liver enzyme levels, and low platelet count (HELLP) syndrome is one of the most severe complications of hypertensive disorders of pregnancy. HELLP syndrome occurring before 22 gestational weeks (GWs) is extremely rare, and patients prevalently exhibit underlying maternal diseases or fetal abnormalities. Here, we report the case of a pregnant woman who had HELLP syndrome at 20 GWs without any obvious underlying maternal diseases or fetal abnormalities. A 38-year-old pregnant woman was referred to Kobe University Hospital from another hospital at 19 + 5/7 GWs for hypertension, proteinuria, generalized edema, and fetal growth restriction. She was diagnosed with partial HELLP syndrome according to the Mississippi classification at 20 + 2/7 GWs. The patient was managed following the Mississippi protocol, including intravenous dexamethasone, magnesium sulfate, and antihypertensive drugs. She received intensive blood pressure and laboratory data monitoring using an arterial line and additional treatments, including platelet transfusion, intravenous haptoglobin infusion, and human atrial natriuretic peptide. The pregnancy ended in an induced delivery at 20 + 3/7 GWs, and she was discharged without complications 10 days postnatal. We performed laboratory tests for diagnosing underlying diseases but identified no obvious underlying diseases. This report indicates that early and intensive treatment of patients with HELLP syndrome occurring before 22 GWs according to the Mississippi protocol may enable clinicians to complete pregnancy termination without maternal complications and provide useful information to clinical practitioners in perinatal medicine.