The urine excretion of L-carnitine (LC), acetyl-L-carnitine (ALC) and propionyl-Lcarnitine (PLC) and their relations with the antioxidant activities are presently unknown. Liquid L-carnitine (2.0 g) was administered orally as a single dose in 12 healthy subjects. Urine concentrations of LC, ALC and PLC were detected by HPLC. Superoxide dismutase (SOD), total antioxidative capacity (T-AOC), malondialdehyde (MDA) and nitrogen monoxidum (NO) activities were measured by spectrophotometric methods. The 0~2 h, 2~4 h, 4~8 h, 8~12 h, 12~24 h excretion of LC was 53.13Ã‚±31.36 Ã‚Âµmol, 166.93Ã‚±76.87 Ã‚Âµmol, 219.92Ã‚±76.30 Ã‚Âµmol, 100.48Ã‚±23.89 Ã‚Âµmol, 72.07Ã‚±25.77 Ã‚Âµmol, respectively. The excretion of ALC was 29.70Ã‚±14.43 Ã‚Âµmol, 80.59Ã‚±32.70 Ã‚Âµmol, 109.85Ã‚±49.21 Ã‚Âµmol, 58.65Ã‚±18.55 Ã‚Âµmol, and 80.43Ã‚±35.44 Ã‚Âµmol, respectively. The urine concentration of PLC was 6.63Ã‚±4.50 Ã‚Âµmol, 15.33Ã‚±12.59 Ã‚Âµmol, 15.46Ã‚±6.26 Ã‚Âµmol, 13.41Ã‚±11.66 Ã‚Âµmol and 9.67Ã‚±7.92 Ã‚Âµmol, respectively. The accumulated excretion rate of LC was 6.1% within 24h after its administration. There was also an increase in urine concentrations of SOD and T-AOC, and a decrease in NO and MDA. A positive correlation was found between urine concentrations of LC and SOD (r = 0.8277) or T-AOC (r = 0.9547), and a negative correlation was found between urine LC excretions and NO (r = -0.8575) or MDA (r = 0.7085). In conclusion, a single oral LC administration let to a gradual increase in urine L-carnitine excretion which was associated with an increase in urine antioxidant enzymes and the total antioxidant capacities. These data may be useful in designing therapeutic regimens of LC or its analogues in the future.