Post-juvenile molt of Common Snipe was investigated during 2004-05 at the Jeziorsko reservoir, central Poland. Body mass and mass of fat stores were dependent on the stage of post-juvenile molt. The body mass increased prior to the commencement of molt, but during the intensive stage of the process it decreased and returned to the previous level. Fat-free body mass increased during molt, which may be attributed to increased protein synthesis or the higher water content of growing feathers. Fat stores were similar in snipe before and in the initial stage of molt; however, they decreased significantly during the transition to the intensive stage of the process. In total, snipe lost approximately 57% of the mass of fat loads over the course of molt (4.9% of lean body mass). Being a highly energetic constraint, post-juvenile molt is suggested to affect certain life history traits of Common Snipe such as the length of the staging periods during the autumn migratory period.