This study investigated the physico-chemical property of the sludge contained uranium in lagoons of uranium conversion plant. The lagoon sludges consist mainly of NH4NO3, NaNO3, Ca(NO3)3, and CaCO3. The data of these compounds' physico-chemical and thermal decomposition properties was obtained from TG/DTA and others. The properties of lagoon sludge were confirmed from these physico-chemical properties data. These will be used for the treatment process of sludge.