Urea transformations in two Andisol-type soils of the Lake Región of Chile were studied. Urea-treated soils were incubated in order to determine the resulting mineral formsof N, interchangeable Al, and pH. ln addition, small posts were used to observe the effects of N applications, as urea and NaNO3, upon plani growth. Results show a fast hydrolysis of urea dueto the high urease activity of these soils. Nitrification is temperature dependent, so thai the time needed to accomplish this process is reduced to it.s half when an increase of 10ºC occurs. The application of urea ends up in a high acidification, mainly in the Nueva Braunau-type soils. Under certain managemeni conditions, the acidifying effect of urea in some naturally occurring low pH Andisols, might cause a detrimental effect upon productivity of some crops.