Benthic diatoms constitute the primary diet of abalone during their early stages of development.To evaluate the dietary preferences of early post-larval abalone,Haliotis diversicolor supertexta,we analyzed the gut contents of post-larvae that settled on diatom films.We compared the abundance and species diversity of diatom assemblages in the gut to those of the epiphytic diatom assemblages on the attachment films,and identified 40 benthic diatom species in the gut contents of post-larvae 12 to 24 d after settlement.The most abundant taxa in the gut contents were Navicula spp.,Amphora copulate,and Amphora coffeaeformis.Navicula spp.accounted for 64.0% of the cell density.In the attachment films,we identified 110 diatom species belonging to 38 genera.Pennate diatoms were the dominant members including the species Amphiprora alata,Cocconeis placentula var.euglypta,Cylindrotheca closterium,Navicula sp.2,and A.coffeaeformis.Nano-diatoms(<20 μm in length) accounted for a considerable proportion of the total species number and cell density of the diatom assemblages in the gut contents and on the films.This suggests that nano-diatoms are important to the efficient production of abalone seed.The difference of the composition and abundance of diatoms between in the guts and on the biofilms suggests that early post-larval grazing was selective.An early post-larval abalone preferred nano-diatoms and the genera Navicula and Amphora during the month after settlement. Benthic diatoms constitute the primary diet of abalone during their early stages of development. To evaluate the dietary preferences of early post-larval abalone, Haliotis diversicolor supertexta, analyzed by post-larvae that settled on diatom films. We compared the abundance and species diversity of diatom assemblages in the gut to those of the epiphytic diatom assemblages on the attachment films, and identified 40 benthic diatom species in the gut contents of post-larvae 12 to 24 d after settlement. the most abundant taxa in the gut contents were Navicula spp., Amphora copulate, and Amphora coffeaeformis. Navicula spp. acted for 64.0% of the cell density. The attachment films, we identified 110 diatom species belonging to 38 genera. Pennate diatoms were the dominant members including the species Amphiprola alata , Cocconeis placentula var.euglypta, Cylindrotheca closterium, Navicula sp. 2, and A.coffeaeformis. Nano-diatoms (<20 μm in length) accounted for a considerable propor tion of the total species number and cell density of the diatom assemblages in the gut contents and on the films. This suggests that nano-diatoms are important to the efficient production of abalone seed. The difference of the composition and abundance of diatoms between in the guts and on the biofilms suggests that early post-larval grazing was selective. Ann early post-larval abalone preferred nano-diatoms and the genera Navicula and Amphora during the month after settlement.