Abstract: There are abundant mineral rare earth resources on the ocean floor such as abyssal rare earth mud,polymetallic nodules and cobalt-rich crusts.This paper focuses on the concentration mechanism of rare earth elements(REE) in polymetallic nodules and cobalt-rich crusts.The authors firstly sum up the content of REE and yttrium(∑REY) in polymetallic nodules and cobalt-rich crusts all over the world,finding that the proportions of their heavy REE and yttrium(HEY) are completely higher than 15%.In addition,∑REY in polymetallic nodules and cobalt-rich crusts is generally higher that in abyssal REE-rich muds,and ∑REY in crusts is generally higher than that in nodules.Taking Cook Islands as an example,we study the concentration mechanism of ∑REY in such significant rare earth resources.Analysis shows that there are strong correlations between ∑REY with Fe and P.Also,it is most likely that ∑REY in polymetallic nodules and cobalt-rich crusts is slowly concentrated by means of the adsorption of iron oxyhydroxide colloid.