The objective of this study was to determine the dissolved inorganic carbon (DIC) andpCO2 concentrations in two third order streams in southwestern Amazonia, Brazil. From May2004 to June 2005 water dissolved oxygen, pH, electrical conductivity, temperature weremeasured to stream water chemical and physical description. DIC and pCO2 measurementswere made by headspace extraction and gas samples for pCO2 and DIC extractions were runon an infrared gas analyzer (IRGA, LI-COR Instruments model LI-820). Results indicate arelationship between soil type and water chemistry, where sandy soil stream presented lowerpH than silty soil stream – consequently DIC and pCO2 concentrations also varied with soiltype. Mean DIC concentration for sitly soil stream was 403±130 μM month-1, while sandy soilstream DIC concentration was 170±59 μM month-1. Free CO2 was the dominant form of DICin both streams. Nevertheless, HCO3- contribuition to DIC was greater for the silty soil stream.DIC contentration also varied seasonally with greater values in the drier period. AbsolutepCO2 values were greater for silty soil stream, mean 3067±1228 Iatm month-1 and2321±1020 Iatm month-1 for sandy soil stream. Seasonality, pCO2 was higher in the dryseason in both streams. Our findings have important implications on the role of soil type inwater chemistry and carbon dynamics and also are used in other studies on carbon balance atthe landscape level.