For the purpose of formation of linguistic competence in mentally retarded children, able to produce sentences with verbpredicate construction, 6 moderately mentally retarded children(the age range being from 7 years and five months old to nine years and nine months old, and five of them had Downs' syndrome), who had stayed at the latter stage of single words, and had still failed to produse sentences with syntactic construction, even though they had acquired comparatively many words, were trained under the following 4 stageconstructed training program: 1)formation of concrete material action with objects, 2)construction of sentences on the base of kinematic linear scheme of sentence, 3)construction of sentences on spatial linear scheme of sentence, 4)construction of sentences on the inner speech(mental linear scheme of sentence). As training material, sentences of Agent-Action and Agent-Object-Action construction were used. As their learning abilities had been extremmely low, training with them lasted for over 8 months and they underwent training of 30〜40 sessions during that period. As a result, the generalized competence, enough to produce the sentences with abovementioned constructions, was achieved in five children. And their acquired competence was proved to be generalized and transferable to their learning of sentences of other construction. Analysis of the effect of the training on the progress of sentence comprehension resulted in their abilities of sentence comprehension markedly developed with the progress of competence of sentence production, except with one child, who seemed to have had some disturbance in linguistic memory.