Background: Agitation in mechanically ventilated patients with decreased consciousness is a challenge in the ICU and a threat to the process of mechanical ventilation. On the other hand, controlling agitation through medication and imposing physical limitations is associated with a number of undesirable side effects. Objectives: This study aimed to determine the effect of auditory and tactile stimulation by a family member on the level of agitation in patients with traumatic brain injury (TBI) and decreased consciousness. Methods: This quasi-experimental study was performed on 80 TBI patients with decreased consciousness who were admitted to the ICU of two teaching hospitals in southeastern Iran in 2019. Qualified patients were selected by convenience sampling and then randomized into the intervention (n = 40) and control (n = 40) groups. Data collection tools included a demographic form and the Richmond Agitation and Sedation Scale (RASS). For patients in the intervention group, the researcher first completed the demographic form and the RASS. Then, they underwent the experiment, which consisted of auditory and sensory stimulation by a family member for 10 minutes. After 30 minutes, the agitation level was measured again. This experiment was performed for seven consecutive days between 16:00 and 18:00 o’clock. Patients in the control group, however, did not receive any intervention other than routine care in the ICU. Data were analyzed in SPSS version 21 by using descriptive statistical tests and independent t-test, paired t-test, [analysis of] covariance, and chi-square test at the significance level of P < 0.05. Results: The results indicated no significant difference in the level of agitation in the intervention and control groups between the first and fifth days; however, independent t-tests and analysis of covariance revealed that the patients who received auditory and tactile stimulation on the sixth and seventh days experienced significantly lower levels of agitation than the control group (P < 0.01). Conclusions: Auditory and tactile stimulation by family members is effective in decreasing the agitation of TBI patients with decreased consciousness. Therefore, it is suggested as a helpful intervention in nursing care programs.