OBJECTIVES The purpose of this study was to assess the utility of quality of life (QOL) in prolonged mechanical ventilation patient and determine the difference between patients and their proxies, including family care-givers and nurses. METHODS We collected consecutive subjects who have been under mechanical ventilation over 21 days in three institutions of southern Taiwan. For patients with basic cognition and ability to communicate their responses, we conducted QOL measurements with Taiwan version of EQ-5D by face to face interview and compare with family care-givers and nurses who directly cared them. Multiple linear regression analyses were conducted to determine the risk factors for difference of scores between patients and proxies. RESULTS A total of 71 patients were enrolled. Their mean age was 77 years, 55% were male. 24 patients were able to assess their EQ-5D and 19 patient-family care-giver pairs and 22 patient-nurse pairs were collected, while 47 family care-giver-nurse pairs were collected for patients with unclear consciousness. The mean of utility assessed by the 24 patients was 0.30±0.22. The mean differences were -0.05 ±0.15 and 0.02±0.21, for patient-family care-givers pairs and patient-nurse pairs, respectively. The results of multiple regression showed that the longer the duration of PMV care the higher the preference score for family care-giver to assess the patient's QOL, after adjustment for age and gender. The mean difference between family care-givers and nurses for patients with poor consciousness was 0.02±0.21, and there was no statistically significant variable to explain the difference. CONCLUSIONS The measurement of QOL for patients with clear consciousness under PMV was slightly higher for nurses than those of family care-givers. As the duration of PMV grew longer, family care-giver also adopted an attitude closer to the patient.