BACKGROUND Personal health records (PHR) can be useful in the emergency environment. Accurate patient information has a significant effect on patient survival and prevalence, and it is important for the early emergency treatment and rapid professional care. However, patient information is fragmented and difficult to access and use in the current medical system in which each medical institution manages patient information separately. It also affects patient experience. Therefore, gathering patient’s information and having it being used actively is important and PHR is an effective means for this. Despite the importance of PHR in emergencies, there are few studies related to PHR in emergencies that evaluate patient experience. OBJECTIVE The aim of this study was to introduce the novel mobile PHR (mPHR) platform to emergency environments and to assess user experience. METHODS The study was conducted from October to November 2019. In total, 1,000 patients or carers in the emergency department of 3 hospitals were provided an application-based service called “FirstER”, which was developed to collect and utilize medical information for emergency patients. The inclusion criteria for participants were age over 19 years and a sufficient level of consciousness to use the application. This study was performed as a mixed-method study that included a survey and an in-depth interview. After using FirstER, we checked usability and conducted a survey on the experience of obtaining medical information with a legacy system and FirstER. Additionally, we interviewed 24 of them to gain insights about their experience regarding medical information using FirstER. For quantitative analysis, the results of the survey were analyzed by descriptive statistics (mean, standard deviation) and inferential statistics (linear regression). For qualitative analysis, we determined the keywords and their frequency from each question of the survey and interview. RESULTS In total, 1,000 patients/carers were recruited in this study. Their mean age was 41.4 (SD 13.3). We ascertained participants’ satisfaction with FirstER and their needs on mPHR through a survey and an in-depth interview. Mean SUS was 67.1 (SD 13.8), which was considered as very near to acceptable. CONCLUSIONS This study was the first one to implement mPHR in the emergency department of large tertiary hospitals in the republic of Korea. FirstER was found to enhance user experience in emergencies in that it provided necessary medical information and proper user experience. Moreover, the average SUS was 67.1, meaning the participants found FirstER to be very near to acceptable. This is very encouraging in that FirstER was developed within a very short time and it was a pilot study. CLINICALTRIAL Study to Evaluate Satisfaction Using Personal Health Wallet Service Clinicaltrials.gov NCT04180618 https://register.clinicaltrials.gov/prs/app/action/SelectProtocol?sid=S0009EXW&selectaction=Edit&uid=U0004LRQ&ts=90&cx=p42jz5