Background/Objectives: In the present study, the changes in oxytocin (OXT) and serotonin (5-HT), as hormones involved in social relationships and mood regulation, respectively, were measured in dialysis patients involved in Animal Assisted Activity (AAA) interventions. Methods: Thirty patients (15 men and 15 women) with chronic kidney disease, undergoing hemodialysis three times per week, for 4 h, were enrolled. The patients were divided into three groups: two experimental groups who received the AAA intervention and a control group that never received the AAA intervention. A specific dog-zootherapist vet pair was assigned for each experimental group. All sessions of the two experimental groups were performed weekly, for a total period of 3 months (12 sessions). Blood samples were collected at the beginning and end of each session (T₀ and T₁), lasting about one hour. The interaction time with the dog was approximately 40 min. The samples were then analyzed to measure the levels of oxytocin and serotonin and processed using analysis of variance with mixed effects models. Results: The results obtained showed that both dog-zootherapist vet dyads caused a statistically significant overall effect of both oxytocin and serotonin, increasing during the sessions, compared to the control group. In addition, it was observed progressively increasing effect between two consecutive weeks. Conclusions: The results from this study showed that the AAA represents a positive stimulus for patients on dialysis. Thus, our study suggests that structured AAA intervention in a hemodialysis center can improve patients’ quality of life during the dialysis cycle.