--- - |2 Abstract This study is the first attempt to measure reactive and proactive aggression in 1,203 youths aged between 11 and 20 from Hong Kong, mainland China, Spain, and Uruguay using the reactive‐proactive aggression questionnaire (RPQ). The two‐factor RPQ construct was found to exhibit an excellent model fit for all subsamples, and the measurement and structural invariance across the four regions was also revealed. After controlling for age, the youth in Uruguay exhibited the highest levels of general, reactive, and proactive aggression, followed by Spain, Hong Kong, and mainland China. Reactive, proactive, and general aggression increased with age in the total sample, but the effects differed among regions. Boys were found to exhibit higher levels of general, reactive, and proactive aggression than girls only in Uruguayan sample. These findings confirmed the cross‐cultural generalizability of the two‐factor RPQ model, and suggested culture, age, and gender to be significant determinants of youth aggression. - Social Development, Volume 27, Issue 4, Page 748-760, November 2018.