Velvet bean (Mucuna pruriens L.) has been found that the degree of suppression on the lettuce root growth by velvet bean was less on the 3D-clinorotation. The number and growth of adventitious root in velvet bean differed among the clinostated and control group. L-DOPA (L-3,4-dihydroxyphenylalanine) is known to be the major substance in the allelopathy of velvet bean plant, released from its root. Since L-DOPA is a precursor of melanin pigment, and is easily converted to melanin by oxidation, locality of L-DOPA production in the plant body can be seen through pigmentation. The amount of L-DOPA was analyzed by HPLC and LC-ESI/MS. The distribution of L-DOPA in the root was different among the ground control condition and pseudo-microgravity.