The soil is the most important carbon reservoir, but agricultural practices involved in tillage systems decrease the soil carbon stock. This study aims to evaluate the effect of no-tillage (NT) on carbon and microbiological attributes of the soil in corn plantations in Manaus-AM, Brazil. Soil was sampled in a secondary forest (SF) and in corn grown under different tillage systems, including conventional tillage (CT), which makes use of plowing and harrowing operations, and no-tillage (NT). Soil variables studied included, carbon content, soil microbial carbon and basal respiration, metabolic and microbial quotients. The data were analyzed by analysis of variance and Tukey's test. The results demonstrated that NT resulted higher carbon, lower basal respiration, and lower metabolic quotient than CT and SF. However, soil microbial carbon was similar in all tillage systems studied. We conclude that NT corn cropping increased soil carbon content more than CT, while it decreased basal respiration and metabolic quotient when compared to NT and SF. Moreover, soil microbial biomass in corn was similar in all tillage systems studied. This research demonstrated the importance of NT to soil carbon conservation and soil management in corn cropping.