ObjectiveTo analyze the correlation of seminal plasma free testosterone and free L-carnitine with semen density, vitality, and motility, so as to investigate their effects on male fertility and their roles in the examination and treatment of male infertility.MethodsUsing chemiluminescence immunoassay method, LC-MS-MS and computer-assisted semen analysis system, we examined the seminal levels of free testosterone, free L-carnitine and sperm density, vitality, and motility in 192 infertile males (normozoospermia, n=36; oligozoospermia, n=48; asthenozoospermia, n=60; and oligoasthenozoospermia, n=48). The difference of free testosterone and free L-carnitine levels between different groups was analyzed, and the correlation of their levels with semen density, vitality, and motility was also analyzed using the SPSS 13.0 statistical software.ResultsThe levels of free testosterone and free L-carnitine in the seminal plasma of the normozoospermia men were significantly higher than those of others (P<0.05).Correlation analysis showed that there was positive correlation between seminal free testosterone with the sperm density (r=0.427, P<0.05), seminal free L-carnitine with the sperm density (r=0.318,P<0.01), and seminal free L-carnitine with sperm vitality, motility (r=0.641, P<0.01;r=0.568, P<0.01).ConclusionSeminal free testosterone level is correlated with the sperm density, and seminal free L-carnitine level is correlated with sperm density, motility and vitality; both levels can be taken as a biochemical index for the clinical diagnosis and treatment of male infertility.