In Lewy body diseases (LBDs), non-motor communication impairments remain relatively underexplored. This study aimed to characterize language deficits in Czech-speaking patients with mild cognitive impairment associated with LBDs (MCI-LB) and elucidate their neural underpinnings. LBD-MCI is characterized particularly by network-specific reductions in dorsal language stream efficiency and functional connectivity underpinning syntactic and phonological processing deficits.