Data are from a randomized complete block experiment at La Selva Biological Station, Costa Rica. Data obtained by a wet-slaking method include the fraction of total soil contained within each of five size categories of macroaggregates (0.25-0.5, 0.5-1.0, 1-2, and 2-4 mm diameter) in the 0-15 cm depth interval under four mono-dominant 25-yr-old tree plantations, an unplanted Control, and the adjacent mature forest. Data also include the following variables regarding the macroaggregates in this experiment: carbon, nitrogen, organic and inorganic phosphorus concentrations and mass per g soil and C:N. Soil pH (0-15 cm) was measured for bulk soil. The planted (dominant) tree species in the plantations were: Hieronyma alchorneoides; Pentaclethra macroloba; Virola koschnyi; and Vochysia guatemalensis.