Collagen is a valuable biopolymer in many fields, especially in biomedical sciences. Thanks to its biodegradability and high biocompatibility, it is a desirable material for applications that require contact with the human body. There are many sources of collagen, of which marine-origin collagen has become an important one in recent times. Pure collagen has poor stability and is sensitive to the effects of heat and other external factors. The cross-linking process can improve the properties of collagen materials. Many different methods of cross-linking can be distinguished, including chemical ones. In this study, we were concerned to obtain collagen films modified with glutaraldehyde (GTA). The influence of this additive on the chemical, mechanical, swelling, and hydrophilic properties of the biopolymeric matrix was evaluated. Two different concentrations of collagen were used, as well as three different concentrations of GTA. Results of the analysis showed that the properties of the obtained films were affected by the addition of even a small amount of cross-linker. Spectroscopic measurements indicated minor changes that reflect interactions between GTA and the collagen matrix. Mechanical tests showed changes for modified samples in values of tensile strength, breaking force, and elongation at break. The hydrophilicity decreased slightly for films with GTA. The durability of the modified samples in the swelling test increased. Differences between 1% and 2% collagen films with additives were also observed. The GTA-obtained fish collagen films can be promising materials for biomedical applications.