The aim of this thesis is to verify sentence imitation as a clinical marker of specific language impairment while controlling memory and morphological richness account as an explanation of problems with acquisition of grammatical markers in preschool children with SLI (basis of these assumptions is explained in the theoretical part of this work). The practical part of this thesis is based on the existing research in Hungarian (Leonard et al., 2009). In contrast to results in Hungarian research the support of morphological richness account is only limited in Czech. Children with SLI were as accurate as younger typically developing children in completions of target forms of verbs and nouns, while completions of target verbs were more successful than completions of target nouns. Near miss errors were prevalent, but not without exception, and relationship between substitutions and frequency in non near-miss errors was not proved. The sentence imitation turned out as a good clinical marker of SLI.