Objective To determine the prevalence of olfactory dysfunctions, mainly, anosmia and to identify its associated factors in patients with COVID-19 infection. Study design A hospital-based prospective observational cohort study Setting A COVID dedicated hospital, Square Hospitals Ltd., Dhaka, Bangladesh. Methods We collected patients information including laboratory-confirmed COVID-19 test results. We used Pearson Chi-square test and logistic regression model to assess the associations between demographic and clinical characteristics and olfactory outcomes. Results Out of 600 COVID-19 positive patients, 38.7% were diagnosed with olfactory dysfunction. Our analyses showed that patients age, smoking status, cough, dyspnea, sore throat, asthenia, and nausea or vomiting were significantly associated with the anosmia. We observed the risk of developing anosmia was greater in younger patients than in older patients, and this risk decreased as age increased [odds ratio (OR) range for different age groups: 1.26 to 1.08]. Smoking patients were 1.73 times more likely to experience anosmia than non-smoking patients [OR=1.73, 95% confidence interval (CI) = 1.01-2.98]. In addition, patients complained asthenia had a significantly double risk of developing the anosmia [OR = 1.96, CI = 1.23-3.06]. Conclusions Our study shows that about 39% of patients diagnosed with olfactory dysfunction. Patients age, smoking status, and asthenia are significantly positively associated with the anosmia. Since anosmia can be a significant marker for the diagnosis of COVID-19, we suggest regular screening of olfactory dysfunction in patients with early symptoms of COVID-19, particularly younger patients, smoker, and complained asthenia.