The human semen ejaculated in a form of liquid state, coagulates immediately after ejaculation, and then liquefies again. However, the mechanisms of neither coagulation and liquefaction of semen have not been explained clearly so far, and very limited numbers of report are available, although the spermatology and andrology made rapid progress. This clinical study has been undertaken to investigate the liquefaction phenomena and practicability of the results might be applied to fertility and infertility problems. As a preliminary study, in this report the liquefaction time of various semen groups is measured and analysed. The following results are obtained: 1. An average liquefaction time of semen of a total of 60 subjects: 25 minutes. 2. An average liquefaction time of semen according to sperm count: 1) Normospermia group (20 cases): 34 minutes. 2) Oligospermia group (20 cases): 21 minutes. 3) Azoospermia group (20 cases): 20 minutes. 3. An average liquefaction time of semen according to abstinence period: 1) Less than 3 days group (30 cases): 22 minutes. 2) More then 5 days group (30 cases): 28 minutes. In conclusion: 1. The liquefaction time of semen of the normospermia group is longer than oligospermia group or azoosermia group. 2. The liquefaction time of semen may not be greatly influenced by the various factors such as abstinence period, semen volume, semen pH, age of the subjects and so on. 3. In routine semen analyses, it is recommended to begin the analysis at least 25 minutes after the ejaculation. 4. Further studies are required in conjunction with practical application of liquefaction mechanism in infertility and fertility control.