The given article dwells on the issues beset with comparative analysis of morphological peculiarities and level of usage of superlative degree of adjective in the Tajik literary language referring to 18th and 20th centuries on the example of the historical productions [1; 2; 10]. It is noted that in the Tajik literary language comparative and superlative degrees are expressed in two ways: synthetic and analytical ones and the theme explored is of a long history and passed various periods and evolution throughout its historical development. Adducing the results of the analysis concerned with the theme explored one can come to the conclusion that in the literary language of 18th and 20th centuries, the superlative degree of adjective is evinced analytically. The superlative degree of adjective is formed by dint of the suffix –tarin in the language of the compared historical productions, it possesses certain common and distinctive peculiarities, on the whole. Thus, in the language of the compared historical productions belonging to the relevant periods, the suffix -tarin is used to express the superlative degree in [10] twice (4 %), in [1] 35 instances (69 %) and in [2] 14 instances (23 %).