The effects of annealing on the fine structure and moisture regain of nylon 4 copolymer films were investigated in terms of the content of nylon 4. Nylon 6-ran-nylon 4 (50/50), (30/70), and (0/100) films were prepared using melt pressing and solution casting methods, respectively. The (N6-ran-N4) copolymer films were annealed in a silicon oil bath at 50, 75, 100, 125 and $150^{circ}C$, and the properties of resultant film were examined by WAXD, DSC, DMTA and moisture regain. The crystal structure in (N6-ran-N4)(50/50) and (30/70) films with increasing annealing temperature was very similar to the gamma phase of nylon 6. The thermal property of (N6-ran-N4)(50/50) and (30/70) films annealed under high temperature exhibit an increase in melting temperature and enthlapy. The result of the tan ${delta}$ behavior of (N6-ran-N4)(0/100) film was confirmed to the appearance of two ${alpha}$ transition peaks. The moisture regain of (N6-ran-N4) copolymer films, except in the case of (N6-ranN4)(30/70) films, decreased when the annealing temperature was increased.