The total amount of ammonia nitrogen (TAN) leaching from Atlantic salmon (Salmo salar L.) feed pellets was determined under controlled laboratory conditions. The leaching was successfully explained by means of a first order kinetic equation: inline image, where a was the maximum TAN leached and k was the velocity of the process. Then ta was defined as the time at which a was reached, which was obtained from the equation prediction. The interaction between pellet size and immersion length significantly influenced TAN leaching: the smaller the pellet and the longer the immersion times, the higher the leaching (a). However, pellet size did not influence k or ta, although k tended to be higher and ta lower for larger pellets. TAN leaching from feed pellets depends on the protein content and contact surface. As the surface/volume ratio (S/V) increases with pellet size while the protein content decreases, it was hypothesized that S/V influences k whereas the protein content has a greater effect on a.