A 56-d feeding experiment in an indoor flowing-through water system was conducted to evaluate the effects of arachidonic acid (ARA) in diets on the growth performance, antioxidant capacity, and body wall fatty acid composition of sea cucumbers () with initial weights of (10.78 ±0.06) g. Six isonitrogenous and isoenergetic diets with varying levels of dietary ARA[0.02% (control group), 0.17%, 0.36%, 0.51%, 0.59%, and 0.98%] were formulated. The ARA content had no significant effect on survival rate (87.50%-94.17%; >0.05). However, both growth rate (WGR) and feed efficiency (FE) increased with increasing ARA content until reaching peak levels at 0.51% dietary ARA, but decreased thereafter (<0.05). Body wall composition analysis indicated that the whole-body lipid content initially decreased but then increased with increasing dietary ARA, whereas the whole-body protein, ash, and moisture contents were unaffected. Superoxide dismutase (SOD), catalase (CAT), and total antioxidant capacity enzyme (T-AOC) activities in the intestinal tract initially increased with increasing ARA content but then decreased (<0.05), whereas the malondialdehyde (MDA) content of the intestinal tract exhibited a contrasting pattern (<0.05). Fatty acid synthase (FAS) and acetyl-COA carboxylase (ACC) activities in the intestinal tract were unaffected when dietary ARA content decreased from 0.02% to 0.59% but decreased significantly when the dietary ARA content increased from 0.59% to 0.98% (<0.05). The ARA and n-6 PUFA contents of the body wall increased with increasing dietary ARA, whereas the EPA and DHA content of the body wall decreased. Therefore, dietary ARA contents of 0.36%-0.51% could be used to promote the growth performance and intestinal antioxidant capacity of sea cucumbers under experimental conditions. The effects of ARA level in diet on the activities of fatty acid synthase, acetyl-CoA carboxylase, and carnitine palmitoyltransferase-1 in the intestinal tract of sea cucumber were also observed in the study.