Abstract: Juvenile kuruma prawn, Marsupenaeus japonicus with an initial weight of 1.64±0.69 g were reared on pellets supplemented with 300, 600 and 1200 mg kg-1 L-carnitine for 8 weeks in 1.2 m diameter round concrete tanks. The results showed that L-carnitine supplementation did not influence weight gain and survival rate at the end of the 56 days feeding period compared with the control group (p>0.05). However, muscle proximate composition of the juveniles was significantly affected by L-carnitine supplementation (p<0.05). Lipid level decreased whilst protein content increased in those fed either 300 or 600 mg kg-1 L-carnitine. At the end of the feeding trial, the shrimp exposed to a cold shock to examine their tolerance. No significant effect of L-carnitine on cold tolerance M. japonicus juveniles was observed.