To alleviate late-onset hypogonadism, testosterone treatment is offered to suitable patients. Although testosterone treatment is commonly given to late-onset hypogonadism patients, there remains uncertainty about the metabolic effects during follow-ups. We assessed the associations between testosterone treatment and wide range of characteristics that included hormonal, anthropometric, biochemical features. Patients received intramuscular 1,000 mg testosterone undecanoate for 1 year. Patient anthropometric measurements were undertaken at baseline and at each visit, and blood samples were drawn at each visit, prior to the next testosterone undecanoate. Eighty-eight patients (51.1 ± 13.0 years) completed the follow-up period. Testosterone treatment was associated with significant increase in serum testosterone levels and significant stepladder decrease in body mass index, total cholesterol, triglycerides and glycated haemoglobin from baseline values among all patients. There was no significant increase in liver enzymes. There was an increase in haemoglobin and haematocrit, as well as in prostate-specific antigen and prostate volume, but no prostate biopsy intervention was needed for study patients during 1-year testosterone treatment follow-up. Testosterone treatment with long-acting testosterone undecanoate improved the constituents of metabolic syndrome and improved glycated haemoglobin in a stepladder fashion, with no adverse effects.