Abstract: There is provided an alumina fiber capable of fixing a honeycomb carrier while maintaining elasticity for a long period of time even in a severe usage environment, and an alumina fiber aggregate formed of the fiber. Problems in a gripping material of an automotive honeycomb carrier are solved by applying an alumina fiber containing from 70 to 98% by mass of alumina and from 2 to 30% by mass of silica, having an average fiber diameter of from 3.0 to 8.0 ?m, a ratio of fibers having a fiber diameter exceeding 10 ?m being 5% or less in terms of the number of fibers and a size of a mullite crystallite contained in each fiber of from 10 to 1500 ?, and by forming an alumina fiber aggregate by using the fibers.