Abstract Menzerath-Altmann law (MAL) describes the relationship between the size of the construct and of its constituents, where the larger the whole, the smaller its parts. Despite numerous investigations dedicated to MAL, few studies have observed the relationship syntactically, especially at the clause level. The present study investigates three units in which clauses in English can be measured, i.e., argument, phrase, and word, by fitting MAL to the relationship between the size of the clause and its constituents. Results show that 1) clause length in phrases can be well fitted by probability distributions, while the goodness-of-fit is less favorable for clause length in arguments and words. 2) MAL holds reasonably well between the size of the clause in phrases and of the phrase in words under some conditions, i.e., within a specific range of construct size and text genres. 3) To summarize, the phrase, a notion proposed by Mačutek, Ján, Radek Čech & Jiří Milička. 2017. Menzerath-Altmann law in syntactic dependency structure. In Proceedings of the fourth international conference on dependency linguistics (Depling 2017), 100–107 under the theoretical framework of dependency grammar, is the most appropriate one to be the neighboring unit of the clause among the three measurement units. These findings may shed light on the features of syntactic structures and lead to a better understanding of the human language system.