The article tries to determine whether and to what degree the qualitative change of the Latin American regional-security complex occurred due to the occurrence of UNASUR and the CDS. The article especially tries to determine the impact of the possible Mexican membership in UNASUR and its influence on the coherence of the LA regional-security complex. The article applies the method of discourse analysis and analyses the key Brazilian political figures’ speeches in order to determine why the Mexican membership in UNASUR poses a securitization issue for Brazil. While presuming that the coherence of the regional-security complex increases when certain issue is interpreted as a securitization issue by all the members of the regional-security complex, the article also focuses on the other UNASUR’s members’ attitudes toward the Mexican membership in this organization.