The present study was designed to investigate whether the retroactive inhibition originally observed in paired-associate learning of nonsense syllables can be generalized to the free-recall learning of sentences. The subjects learned two lists of 12 sentences in succession. The syntactic structure of each sentence consisted of a noun phrase and a verb phrase, and two free-recall lists were constructed to conform the A-B, A-D and A-B, C-D paradigms. The major results indicated that (1) substantial retroactive inhibitions (RIs) occurred in both transfer paradigms; (2) these RIs were overcome by using relevant knowledge to integrate sentences; and (3) the subjects could recall the constituents of a sentence (noun phrase and verb phrase) even when they could not recall a whole sentence. These results were interpreted as contradicting the classical interference theory in which RI would be predicted on the basis of A-B, A-D relationship between successive lists, and the theoretical implications for the models of sentence memory were discussed.