Resumo. The fixed carbon concept is normally related to the idea of storing carbon in forest soil and other vegetations type. This research aimed the modeling of total above ground organic carbon and also for the firewood component by unit of area fixed in Mimosa scabrella stands in the metropolitan region of Curitiba. The database came from 272 temporary sample plots with ages ranging from 3 to 18 years. It was tested 21 traditional models: 10 arithmetic ones and 11 logarithmic ones; it was also developed models by Stepwise process from a correlation matrix. The equation of best performance was chosen based on R²aj, Syx%, F value and on graphic analysis of residuals. A simple linear correlation between the used variables differed from those traditionally found results for volume of stands. This result was also observed in the fitting of mathematical models by stepwise, in which the variable average height didn’t compose any adjusted model. Although efficient, selected traditional equations were less accurate than the equations adjusted by stepwise, reinforcing the importance and improving that this method represents to modeling studies.