A new digamasellid mite, Longoseius (Longoseiulus) disparisetus sp. nov., was described from females found in the wood detritus of tree cavity of freshly felled elm (Fraxinus sp.) in a park in southwestern Slovakia. The new species differs from known congeners by the number of setae on some leg segments (genu II with eight setae, tibiae II and III with seven and six setae, respectively) and by the unusual presence of three pairs of conspicuously shortened setae (J3, J4, and Z3) on the posterior dorsal shield. In other known Longoseiulus species, the genu II has 11 setae, the tibiae II and III have 10 and seven setae, respectively, and almost all dorsal setae are of similar length (except for the elongated Z4 and S4), none of which is formed as a microseta. A dichotomous key for females is provided to identify species classified worldwide in Longoseiulus.