The designation of the oldest mosque in the world requires careful use of definitions, and must be divided into two parts, the oldest in the sense of oldest surviving building, and the oldest in the sense of oldest mosque congregation. Even here, there is the distinction between old mosque buildings that have been in continuous use as mosques, and those that have been converted to other purposes; and between buildings that have been in continuous use as mosques and those that were shuttered for many decades. In terms of congregations, they are distinguished between early established congregations that have been in continuous existence, and early congregations that ceased to exist (wikipedia). More after the break.
01. Quba Mosque, Saudi Arabia
First Built: 622
02. Al-Masjid al-Nabawi, Saudi Arabia
First Built: 622
03. Masjid al-Qiblatain, Saudi Arabia
First Built: 623
04. Jawatha Mosque, Saudi Arabia
First Built: 629
05. Masjid al-Haram, Saudi Arabia
First Built: 638
06. Great Mosque of Kufa, Iraq
First Built: 639
07. Mosque of Uqba, Tunisia
First Built: 670
08. Imam Hussain Mosque, Iraq
First Built: 680
09. Al-Aqsa Mosque, Jerusalem
First Built: 705
10. Al-Zaytuna Mosque, Tunisia
First Built: 709
source: http://coolfunclub.blogspot.com/2011/02/10-oldest-mosques-in-world.html
