The invention relates to a system for injecting liquid precursors in gaseous and/or vapour state, in nanoparticle synthesis by laser pyrolysis. According to the invention, the system consists of two injection tubes (1 and 2) with accumulation chambers for flow uniformization, with adaptable geometry and adjustable geometrical position in respect of the optical axis of the laser beam and with a mutually adjustable position, an injector body (3) with precursor-specific ducts, which is heat insulated from a reaction chamber (5) by means of a ceramic material (6) of reduced dilation coefficient, a heat-insulated closed enclosure (7) in which there is a hot air generator (GAC) which delivers hot air at preset flow-rate and temperature, while the temperature of precursors (P) and of some confining/technological gases ( C) is monitored, by means of two thermocouples (TC1 and TC2), by a temperature control unit with two thermostats controlling the hot air generator (GAC).