Inclusion Criteria:  1. Subjects with NAFLD determined by MRI-PDFF (liver fat>5%).  2. Subjects with BMI<23 kg/m2.  3. Subjects with inactive exercise before.  4. Subjects with basic abilities of understanding, communication and writing.  Exclusion Criteria:  1. Regular drinkers (consumed more than an average of 140 grams of ethanol per week in men and 70 grams in women during the past twelve months).  2. Complicated with other liver diseases (i.e. acute or chronic viral hepatitis, liver cancer, liver cirrhosis, drug-induced liver diseases, and autoimmune hepatitis).  3. Subjects with abnormal liver function (i.e. more than 3 times the upper limit of normal alanine aminotransferase and aspartate aminotransferase).  4. Complicated with severe cardiovascular disease [i.e. myocardial infarction, arrhythmia, heart failure (New York Heart Association III or IV), uncontrolled hypertension (i.e. systolic blood pressure >180 mmHg, and/or diastolic blood pressure >100 mmHg)].  5. Complicated with severe kidney disease or severe renal insufficiency or tumour.  6. Currently pregnant or planning to be pregnant or breast feeding women.  7. Participating in weight loss programs/exercise programs currently or during the past three months.  8. Having any medical condition that would affect metabolism or limit exercise (i.e. diabetes, known hyperthyroidism or hypothyroidism).  9. Having a medical condition that would limit exercise participation or alter heart rate during exercise or taking medication that would affect metabolism or weight loss (i.e. glucocorticoids, antithyroid drugs, hypoglycemic drugs, antihypertensive drugs).  10. Having been doing regular physical exercise for the past three months (i.e. 3 times/week, >30 min/time).  11. Subjects with poor adherence.