Methylphenidate (MPH), commercially called Ritalin or Concerta, has been widely used as a drug for Attention Deficit Hyperactivity Disorder (ADHD). Noteworthily, growing numbers of young people using prescribed MPH improperly for pleasurable enhancement, take high risk of addiction. Thus, understanding the mechanism underlying high level of MPH action in the brain becomes an important goal nowadays. As a blocker of catecholamine transporters, its therapeutic effect is explained as being due to proper modulation of D1 and α2A receptor. Here we show that higher dose of MPH facilitates NMDA-receptor mediated synaptic transmission via a catecholamine-independent mechanism, in layer V-VI pyramidal cells of the rat medial prefrontal cortex, using in vitro whole-cell patch-clamp recording technique. To indicate its postsynaptic action, we next found that MPH facilitates NMDA-induced current and such facilitation could be blocked by sigma-1 but not D1/5 and α2 receptor antagonists. And this MPH enhancement of NMDA-receptor activity involves PLC, PKC and IP3 mediated intracellular Ca2+ increase, but does not require PKA and extracellular Ca2+ influx. Our additional pharmacological studies including western blot analysis and receptor binding assays, confirmed that higher dose of MPH increases locomotor activity via interacting with sigma-1 receptor. Together, the present study demonstrates for the first time that MPH facilitates NMDA-receptor mediated synaptic transmission via sigma-1 receptor, and such facilitation requires PLC/IP3/PKC signaling pathway. This novel mechanism possibly explains MPH-induced addictive potential and other psychiatric side effects.