In this study, the effect of tool rotational speed (1230, 1450 and 1670 rpm) on the tensile properties of AA7075-T6 aluminum alloy was investigated after natural aging. The total elongation (TE) of friction stir welding (FSW) specimens was analyzed by Weibull statistics. The TE of 1230R specimens was remarkably higher and more concentrated, while that of 1670R specimens was concentrated but severely deteriorated (2-6.7%, not conducing to applications). Hence, the 1670R specimens were not subjected to Weibull analysis. It is noteworthy that 1450R specimens had larger fluctuations than the others in TE. In addition, the TE distribution of 1230R specimens in this experiment was from 18 to 25% and that of 1450R specimen was from 3 to 24%. The Weibull modulus m for 1230R and 1450R specimens were 3.07 and 0.66, respectively. Thus, 1230R specimens should be considered more reliable in engineering applications. In addition, the microstructures and the EPMA analysis of 1450R specimens confirmed that different fracture behaviors (ductility and embrittlement) were affected by the distribution of the elements, precipitates and metal flow zones. As a result, the TE of 1450R specimens had a large fluctuation range, which decreases reliability.