Testosterone (T) plays a crucial role in spermatogenesis because extremely low levels of intratesticular T lead to correspondingly low serum levels of total T (tT), severe disorders of spermatogenesis, and male sterility. However, there is little consensus on the lower limits of serum tT in proven fertile men undergoing assisted reproductive technology treatments in Chinese or other Asian populations. We aimed to establish the reference range of serum tT based on a population of 868 fertile Chinese men undergoing in vitro fertilization or intracytoplasmic sperm injection and embryo transfer (IVF/ICSI-ET) treatments. We defined a fertile man as having had a live baby with his partner as recorded in our IVF registration system. The lower limits of serum tT were established using a Siemens IMMULITE 2000 chemiluminescent system. The 1st, 2.5th, and 5th percentiles and their 95% confidence intervals (CIs) were 3.6 (95% CI: 2.7-4.1) nmol l-1, 4.3 (95% CI: 4.1-5.0) nmol l-1, and 5.6 (95% CI: 4.8-5.8) nmol l-1, respectively. Using the linear correlation of serum tT between the Siemens platform and a liquid chromatography-tandem mass spectrometry platform, the calculated lower limits of serum tT were also established for fertile Chinese men undergoing IVF/ICSI-ET treatments, which will benefit the clinical diagnosis and treatment of male infertility during such procedures.