Coconut mites (CM), Aceria guerreronis Keifer, are the most notorious and an important pest of coconut crops widespread in almost all coconut producing countries. Although CM has been reported worldwide and has been damaging coconuts, which causes huge losses in coconut production in India, Asian countries and in Europe. The biological control of CM using active entomopathogenic fungi is a good sustainable alternative over the chemical pesticides. The objective of this study were to assess the pathogenicity of an Entomogenous fungus Hirsutella thompsonii against Aceria guerreronis under laboratory conditions, optimization of media for mass production, formulation of product and in-vitro application. Application of formulated product (1 × 107 spores per gram) applied by three different modes viz. Dry (dust), wet (liquid) and wet+ dry. The mite mortality was assessed after four and eight days of inoculation. Among three mode of application wet+ dry mode showed excellent result over others. The mortality percentage after 4 days of incubation was 62% while after 8 days of incubation percentage of mortality rises up to 81 %. This study demonstrates that Hirsutella thompsonii is a promising candidate for the development of biological control agent against coconut Eriophyid Mite.