Understanding the impacts of pasture recovery on soil organic matter accumulation processes is extremely important. For this reason, the quantitative analyses of organic matter are tools capable of evaluating the alteration of the different managements on the processes of formation and maintenance of pastures. The objective of this research was to compare the levels, stocks, and isotopic abundance of carbon and nitrogen in pastures with different years of recovery and secondary forest in eastern Amazon. The following managements were evaluated: secondary forest (SF), perennial pasture (PP), perennial pasture recovered 5 years ago by the intercropping of Corn + Brachiaria brizantha cv. Marandu (ICL5) and recovered 8 years ago by the Corn + Brachiaria brizantha cv. Marandu (ICL8). Contents and stocks of total carbon (C) and nitrogen (T), and abundance of δ¹³C and δ¹⁵N isotopes in different layers were determined. In the ICL8 area, the highest levels of total C and N were observed. The highest levels of total C and N alongside profile were observed in ICL8 treatment. In ICL8 and PP treatments, highest values of C and N were observed when compared to secondary forest. By the natural abundance of δ13C, it was possible to observe the highest enrichment in the PP area, ICL5 and ICL8 intermediate behavior, while in the SF the lowest enrichment. There were no significant differences for δ¹⁵N. The longer recovery time of pastures provided increases in the contents and stocks of C and N in the soil and were able to preserve the stable isotopes of 13C derived from C3 plants in the soil.