The rapidly growing, woody perennial legume, Leucaena (Leucaena leucocephala(Lam.) de Wit), is adaptable to a wide range of neotropical soil conditions. EffectiveRhizobiuminoculation and endophyte mycorrhizal colonization are essential for high levels of production and symbiotic N2fixation. The objective of this study was to determine growth, nodulation, nitrogenase activity and nodule composition of inoculated Leucaena as affected by mycorrhizal colonization and factorial soil fertility treatments of a Typic Eutrustox. Highly significant increases in top growth, nodule fresh wt. and nitrogenase activity resulted withGlomus fasciculatumcolonization, soil K and linear increases with low‐soluble P fertilization to 300 mg P kg‐1soil. Highly significant interactions for increased nodulation and nitrogenase activity resulted with K × mycorrhiza. Interactions of all three factors P, K and mycorrhiza were highly significant for nodule fresh wt. However, responses comparing inoculation withG.fasciculatumand with combinedG.fasciculatum,G.microcarpusandG.claviumwere not significant. Highly significant increases with applied K levels to 300 mg K kg‐1soil resulted with top and root growth, nodulation and nitrogenase when applied with soluble P at 100 mg kg‐1soil and 500 mg Ca kg‐1soil. Significant and highly significant interactions of P, Ca and K level resulted for all parameters. Plant nutrient element composition of nodules increased with the fertilization treatments for P, Ca and increased K levels. A highly significant inverse relation was apparent with decreased Na resulting with increased K levels. Half or more of total nodule K, P and Mg but less than 20% of Ca and Na were within the nodule cytosol. Sodium, Mg, P, and Ca decreased in the cytosol fraction with increased K content.