<p>The aggregate breakup of structured soft clay has an important influence on the properties of the soil. In this paper, the aggregate breakup of structured soft clay under one-dimensional compression is investigated based on FESEM images, and the relative breakage <i>Br</i> is used to assess the degree of aggregate breakup, and the results show that: The structured soft clay consists of dispersed clay particles, clay aggregates and pores. When the soil is loaded, not only pores change but also clay aggregates breakup occurs. The compression process is divided into three stages: initial structured breakup stage, aggregate breakup stage, and compression stabilization stage. The degree of aggregate breakup is increasing with the increase in vertical load, the greater the degree of breakup, the greater the fractal dimension, and the maximum <i>Br</i> is 0.33. The void ratio decreases nearly linearly with the increase of <i>Br</i>, and the compressive modulus changes exponentially when the <i>Br</i> exceeds 0.20. The empirical formulae established can be utilized to predict the void ratio and compression modulus, and provide a reference for studying the aggregate breakup of structured soft clay.</p>