Increase in cyclic strength due to aging of sands is reflected in the higher number of cycles necessary to reach liquefaction. Results are reported from cyclic triaxial tests on reconstituted and undisturbed block samples from the Ovejeria tailing dam. Observations on the change on the cyclic stress ratio caused by aging effects during a period of time between 0 to 5 months enable the characterization and comparison on the cyclic behavior on remolded specimens and in situ samples. The new laboratory data is compared with selected data reported in the literature confirming the relevance of aging effect and a qualitative difference between reconstituted and undisturbed samples. Preliminary observations indicate that cyclic strength of undisturbed samples obtained directly from the tailing dam cannot be compare directly with the strength of reconstituted specimens by moist tamping with the same age. © 2009 IOS Press.