During the AKP era,Turkish-Iranian relations benefit from the new dynamism in regional affairs, especially in the Middle East,based on the pro-active foreign policy approach.In the decades before the AKP government, Iran was perceived by Turkish elites as the ideological other and rival. The decade after the new millennium witnessed a perception change led by Foreign Minister Davuto'luwho replaced the old mindset based on mistrust with a coursecenteredon cooperation in several significant fields. Nevertheless, Iran's disputed nuclear program is an important barrier for closerrelations. Although the Iranian nuclear program is perceived as a serious threat by the international community, Turkey has, in line with the new mindset of cooperation, vigorously advocated the right of Iran to develop peaceful civilian nuclear technology. Thus, Turkey has not suspected Tehran of secret uranium enrichment activities. The Arab Spring was the breaking point in Ankara's miscalculated Iran perception. After a concretization of differences of interests, mainly on Syrian issue, the position of Ankara toward Tehran has noticeably changed. Ankara has realized that the differences with Iran remain despite Turkey's constrictive new Iran approach. A cooperation-oriented relationship has been replaced with a latent conflictual one due to diametrical interests of both countries during and after the Arab Spring, in particular because ofdifferent positions onSyria. After this perception change, Turkey had to respond and take measures, especially in defense policy, which has driven Turkey into more intensive cooperation with the USA and NATO at the expense of her independent proactive regional policy. This article explores the reasons for the persisting and changing perceptions of Turkey on Iran and seeks to analyze the motivations of Turkey's Iran policy as it relates to Ankara's changing security perceptions, in particular with respect to Iranian nuclear and ballistic technology programs.