The research aimed to assess air quality in Mosul city/Iraq using air quality index (AQI). The data were collected at six monitoring sites using two stations, one fixed and the other is mobile type. The concentrations of CO, NO2, O3, SO2 and PM10 were measured. The daily AQI were calculated for each site and classified to AQI categories according to USEPA approach. The dominant AQI category at the public library site fluctuated between "Moderate" to "Unhealthy for Sensitive Groups". AQI undergoes seasonal variation with lower value at March. The results showed that PM10 is the main contributor for AQI determination in Mosul city with 93.8%. CO has no contribution to Mosul AQI. SO2, O3 and NO2 have little contribution to Mosul AQI with 0.8%, 2.7% and 2.7% respectively. The annual mean of AQI in the public library site/ Mosul city is 96 in the category "Moderate. The worst site was Mosul municipality (old location) with a dominant category "Unhealthy for Sensitive Groups".