COVID-19 has been rapidly spreading around the world. To prevent the overflow of the patients in hospital, out-of-hospital isolated & treatment center (ITC) were temporally established for pts with asymptomatic or mild symptoms. We evaluate the natural course of COVID-19 in pts with asymptomatic or mild symptoms administered at ITCs from March-02-2020 were included for analysis. Age, gender, comorbidity, clinical, laboratory, image, treatment and outcome data were collected from retrospective review of medical records. Nasal and throat swap specimens were obtained, and RT-PCR method was used for detecting virus. Finally, data of 632 pts were analyzed. 31 pts (4.9%) showed symptoms at diagnosis, and 259 pts (41.0%) of mild symptoms during follow-up period. 579 pts (91.5%) showed remission and discharged from ITC, and mean duration of remission period was 20.1±7.7 days. 19 pts (3.0%) were transferred to hospital. Age (>50), presences of comorbidity and symptom were significantly correlated with transfer to hospital (p<0.0001, p=0.005, p<0.0001). There showed relatively longer remission period in symptomatic patients than asymptomatic patients (19.1±7.5 vs. 21.7±7.6 p<0.0001). In patients with mild symptoms, mean duration from diagnosis to symptom develop was 10.4±8.6 days and duration from symptom onset to remission was 11.6±8.2 days. It took 2 to 3 weeks from diagnosis to complete remission, and in some patients up to 6 weeks. Symptomatic patients had significantly longer durations to remission than those without symptoms at admission.