Heat-induced gelation mechanism of ovalbumin (OVA) in neutral, salt-free aqueous solution was investigated by dynamic light scattering and small-angle neutron scattering. The scattering profiles obtained from OVA solutions/gels showed a correlation peak. It is clarified that the position of the peaks was independent of the concentration after heating. From this fact, we described the gelation mechanism as a percolation of aggregates. In addition to this, the gelation mechanism of pOVA was also investigated and compared with that of OVA, where pOVA is a large OVA fragment lacking in N-terminal short peptide region. Although the primary structures of OVA and pOVA are almost the same, the scattering profiles obtained from pOVA were totally different from that of OVA. This difference can be explained by the difference of their dispersion states in the solution, which is originated from small difference of their primary structures. (C) 2016 Elsevier Ltd. All rights reserved.