Rubisco activase undergoes ATP hydrolysis to activate Rubisco which has generated an inhibitor. Recent crystallographic evidence has proposed several models however the correct model is disputed. The point of contention involves the active oligomeric state of Rubisco activase. This study indicates that the oligomeric state of spinach Rubisco activase is dependent on concentration, temperature and ligand binding. Rubisco activase appears to exist in a number of oligomeric states, and in polydispersive solutions, of which all appear active. Activity was recorded in concentrations ranging from 0.01 to 0.1 mg.ml-1. SEC, SEC-MALS and DLS indicated that the prominent oligomer present in solution changed through these concentrations from dimers to hexamers. Nucleotide supplementation was shown to cause an increase in molecular weight and thermal stability while Mg2+ was shown to have a minor destabilising effect on both. This data indicates that the oligomeric state of spinach Rubisco activase is dynamic, largely dependent on concentration and ligand association. Comparison of data indicated that a dimer-tetramer is required for activity with a tetramer giving full activity. Critical oligomeric states were also seen at a hexamer and an octamer for thermal stability.