AbstractTemperament has attracted a lot of attention over the years and may be linked to the success or failure in the performance of an L2. The interest brings up the motivation to investigate Learners’ variation, while some are better and some are poor in L2 performance (Ellis, 2008). There have been claims that temperament of a learner determines the failure or success in language learning and use (Pennebaker & King, 1999). This study investigate the influence of temperament of Turkish EFL Learners in L2 achievement, temperament is a major aspect of humans and there have been different argument and to where it originate from either from genes or the environment. Behavioral science is of the view that genes affect temperament than the environment. ‘Heredity has a greater influence on one’s personality and behaviour than either one’s upbringing or the most crushing social pressure’ (Lang, 1987, p.58-66).