Ludwigia grandiflora is an amphibious plant that has been designated as a specific alien plant in Japan. Due to the risk of regeneration on land, plants are burned after eradication. Since L. grandiflora is fertile and rich in biomass, this study investigated the use of L. grandiflora as a feed for ruminants. We measured general components, detergent fiber components, and in vitro dry matter digestibility (IVDMD) using rumen microbes for three forms (terrestrial form, emergent form, and floating‐leaved form) of L. grandiflora. In addition, concentrations of hazardous metallic elements were also measured from the viewpoint of feed safety. Crude protein, neutral detergent fiber, acid detergent fiber, and acid detergent lignin were contained 10.31–14.62, 27.83–42.28, 20.54–36.05, and 6.94–18.90 (%DM), respectively. IVDMD was 50.75%–68.24%. Toxic elements such as Pb, Cd, and Hg were not detected in all forms. These results suggest that L. grandiflora could be partially used as alternative roughage for ruminants.