Background: Transcranial light therapy (TCLT) is a new noninvasive interventional method, which applies red to near infrared spectrum laser or light emitting diode (Led) source on the head, transcranially. This spectrum can penetrate the skull and could improve the brain pathological conditions and cognitive functions. Despite relative advantages of the Led upon laser sources, TCLT research has been limited on the beneficial effects of Led source on human cognitive performances.Objectives: This study aimed at investigating the effectiveness of the TCLT with Led source on brain attentional performance as an important cognitive ability.Methods: This experimental intervention study was conducted in Tabriz, Iran, from September to October 2016. The study samples were selected by the convenience sampling method. Thirty-four healthy individuals (age: 18 to 24; 17 males and 17 females) were randomly assigned to sham (n=17) or real intervention (n=17) groups. We applied 850 nm Led with irradiation energy density 60 J/cm2 upon the frontal cortex, the brain region involved in attentional activities. Before and after TCLT, participants completed a cognitive task (Level-1 of parametric Go/No-task), which measures attentional performance.Results: Our results reveaLed improvement of efficiency score as the main parameter of attentional performance in the real intervention group versus sham-TCLT group. The interaction of grouptime was significant (P=0.004). Mean change of the efficiency score was higher in the real intervention group (mean=4.6±3) than the sham group (mean=0.8±3) after TCLT (P=0.001).Conclusions: Applying the TCLT by Led source over the PFC, promotes attentional performance as an important cognitive function.