To obtain an acaricidal fiber eluting a specific amount of B2O3 on a treatment under specified conditions, improved in the acaricidal characteristics, improved in hot water resistance and capable of giving the sufficient acaricidal effect, also after subjected to a hot water-resistant treatment by kneading a prescribed amount of a specific borate ceramic.

This acaricidal fiber comprises a kind of fiber among polyethylene, polypropylene, a polyester, polyacrylonitrile, vinylon, polyvinyl chloride, polyvinylidene chloride, a polyurethane and a nylon for non-dyeing, which are kneaded with 0.5-10wt.% of a borate ceramic comprising the bound product of B2O3 to CaO and/or the bound product of B2O3 to MgO and having a particle diameter of ≤10μm. The fiber elutes ≥200μg of B2O3 from 1g of the fiber, after immersed in 20°C water for 24hr.