This study was conducted for the purpose of long-term monitoring of changes in the sociability of group-housed cats towards a familiar caregiver in a private no-kill shelter. The sociability of the monitored cat population was assessed at two-week intervals during one calendar year. A total of 158 animals were rated on a 5-point scale, the individual levels of which represented the level of sociability (1-very friendly cat to 5-very unfriendly cat). The evaluation was performed by visual observation of the cats' response to human approach and contact by one observer. At the first assessment, more than three quarters of the cats (81%) showed very friendly (score of 1) or friendly behavior (score of 2). Of the 88 cats that were evaluated at least twice and at the same time their stay in the shelter terminated during the monitoring period, 56 cats (63.6%) did not change their score (worsen or improve) during their stay in the shelter. Among the cats with an observed change, there was a permanently improved score in a significantly higher number of cats (P < 0.001) during the stay in the shelter than a permanent deterioration (26; 29.5% and 3; 3.4%, respectively). There was a temporary improvement or worsening of the score in 3 cats (3.4%). The improvement in the sociability score during the stay in the shelter mainly concerned cats whose behavior was rated as neutral (score of 3), unfriendly (score of 4) or very unfriendly (score of 5) at the first evaluation. The length of stay of cats in the shelter (LOS) correlated with the level of sociability of the cats during the first (rtau = 0.72, P < 0.001) and the last evaluation (rtau = 0.23, P = 0.007); however, the LOS itself did not predict the level of sociability (P > 0.05). The sociability level at the first assessment was found to be a predictor of the sociability level at the last assessment (P < 0.001). The results of our study suggest that during the stay in the shelter, the cats generally improve their sociability towards a familiar person. Although it appears that cats with lower levels of sociability remain in the shelter for a longer period of time, improvements may increase their adoption potential. Support for programs to increase the cat sociability is needed and should be addressed in further research.