Transformation and nitrification of 4 doses of urea and its effect on the growth of nitrifiers were studied using 8 soils of Bangladesh. The dominant ammonium oxidizers present in BAU Farm and Tea soils appeared respectively to be Nitrosomonas and Nitrospira while the other soils seemed to contain Nitrosolobus. However, further studies are required for its confirmation. Urease activity and rate of urea hydrolysis were quite high in most soils except the Kosh and Tea soils. Urea application increased the ammonium concentration in the samples but it disappeared rapidly with the production of nitrite and nitrate. Nitrite was found to accumulate in the calcareous Ruppur, Pakuria and Nurmagor soils due to relatively higher activity of ammonium oxidizers and production of free ammonia. Higher pH and higher ammonium accumulation were not the sole factors for nitrite accumulation. Higher ammonium accumulation was recorded in the Tea and Kosh soils for a longer period. Nitrification of the accumulated ammonium-N resulted in pH decrease in the soils. Nitrifying capacity was high in most samples except the Kosh and Tea soils. Initial population and the subsequent growth of nitrifiers due to urea treatments in Kosh and Tea soils were low due to its higher acidity. The pattern of nitrate accumulation, growth of ammonium and nitrite oxidizers due to urea treatments as a function of incubation time significantly followed a second degree curve in most samples. In few samples the curves skewed to the left or right showing higher and lower rates respectively. Lower productivity ratios and higher deficit of applied urea-N were observed more prominently in the calcareous soils. The ways of loss were volatilization as free ammonia and perhaps also through other gaseous products during nitrification. Germination of jute seeds and growth of its seedlings were adversely affected by free ammonia produced and accumulated nitrite. It was concluded that low efficiency of urea as a fertilizer in most soils of Bangladesh studied is associated with the rapid transformation of urea and higher activity of chemoautotrophic nitrifiers. The causes of low efficiency of urea in Tea and Kosh soils are the delayed transformation of urea and low activity of chemoautotrophic nitrifying bacteria.