Concentrated latex rubber industry is one of the major industries in the Southern region of Thailand. Typically, factories employ pond systems in series to treat large amount of wastewater which contains high organic components. However, the effluent does not meet the Thailand's effluent standards and needs to further treating by other treatment technologies that have ability to degrade the remaining contaminants that cannot be removed by the biological means. Ozonation may be the alternative treatment methods because ozone can directly react with the organic pollutants or indirectly react by hydroxyl radicals result in converting organic pollutants to low molecular weight and ultimately innocuous products such as carbon dioxide (CO2), water (H2O). Laboratory-scale of ozonation was conducted for experiments. Unfiltered and filtered wastewater was used and adjusted pH to about 7 prior to feed to the chamber. The experiments was varied the applied ozone dosages of 0.5:1, 1:1, and 2:1 mg O3/mg COD. Samples were withdrawn for analysis at the contact time of 5, 15, 30, and 60 minutes, respectively. Results of the BOD5/COD ratio of unfiltered and filtered effluent are about 0.14 and 0.10, respectively, indicating that it has substantial amounts of refractory substances that are difficult to be biodegraded. It was found that the removal efficiencies of unfiltered wastewater due to ozonation were independent of ozone dosage. On the other hands, increasing in the ozone dosage resulting in increasing removal efficiencies of ozonation for filtered wastewater.