The objective of this work was to investigate the effect of spreading behavior of the sizing agents (AKD or dialkyl ketone) on the sizing development of AKD-sized paper. There was a direct relationship between the spreading behavior of the sizing agents and their melting points. Both AKD and dialkyl ketone showed no substantial spreading until the temperature reaches to their melting points. Consequently, dialkyl ketone did not provide sizing development when the paper was heat-treated below $75^{circ}C$, while AKD provided sizing effect even the paper heated at $50^{circ}C$. The ketone, however, provided rather higher sizing effect than that of AKD, when the paper was heat-treated over $100^{circ}C$. This result means that the ketone also gives sizing development to paper, moreover the ketone could give higher sizing effect to paper than AKD when it was melted and well spreaded on the fiber surface. While the ketone introduced to papers from hydrolyzed AKD emulsion could not contribute to sizing development.