Embryos of the giant freshwater prawn, Macrobrachium rosenbergii, were treated with 1, 10 or 50 µg ml−1 all-trans retinoic acid (AtRA) for 2 days. Survival and hatching rates were not affected. However, an increase in the number of primordial germ cells (PGCs), progenitors of gametes, and a slightly more advanced stage of the gonads were found in those treated with 10 or 50 µg ml−1 AtRA. Newly hatched larvae were treated with 0.1, 0.5 or 1 µg ml−1 AtRA for 2 days. Survival rates were lower in those treated with 0.5 or 1 µg ml−1 AtRA; nevertheless, the gonads were slightly more developed. The results indicated that AtRA, an active metabolite of vitamin A, affected germ cell and gonad development of embryos and the larvae of giant freshwater prawn.