Rapid urbanization occasioned by population explosion, rural-urban drift and industrialisation in most city centres of developing countries is impacting negatively on the environmental quality of such cities. In this study, the ambient air pollution of the city of Nnewi was assessed using on-site digital read out portable monitor for both dry and wet seasons. The parameters monitored were CO, SO2, NO2, total suspended particulate (TSP), particulate matter with aerodynamic size smaller than ten micrometre, (PM10) and two and half micrometre (PM2.5). The results showed that the mean dry season levels were 0.612±0.35 ppm, 0.146±0.06 ppm, 0.135±0.08 ppm, 105.83±24.98 μg.m-3, 69.46±17.81 μg.m-3 and 26.35±13.40 μg.m-3 respectively; While the corresponding wet season mean values were 0.402±0.27 ppm, 0.074±0.05 ppm, 0.063±0.05 ppm, 46.98±17.25 μg.m-3, 22.35±8.64 μg.m-3 and 4.13±2.86 μg.m-3 respectively. The students t-test for difference in seasonal means of the pollutants showed that their differences were statistically significant (p<0.01). The gaseous and coarse particulate pollutants levels were within the WHO guideline limit for ambient air whereas the fine particulates (PM10, PM2.5) exceeded the WHO guideline limit for 8 hours averaging period.