The objectives of this study is to investigate word formations of comparative forms of adjectivesby suffix [-an] in Toba Batak. Comparative forms of adjectives by suffix [-an] in Toba Batak areconstructed without considering the number of syllables of the base forms of adjectives as those inEnglish. Besides, the attachments of suffix [-an] to adjectives in Toba Batak to constructcomparative forms do not require any phonological rules as those when attaching prefix [um-] toconstruct comparative form in Toba Batak. The stress of the words modified with suffix [-an] is insuffix [-an] itself. The meaning of suffix [-an] denotes comparative forms. It signifies moremeaning than what is indicated in the base forms of the adjectives to which suffix [-an] is attached.In short, word formation of comparative form by suffix [-an] in Toba Batak can be done to alladjective bases in very simple way inflectionally.