NOVELTY - Treating solid urban wastes (RSU), comprises: (F1) providing at least one amount of solid urban wastes RSU (R2); (F3) triturating inert wastes (R1); (F5) separating triturated wastes (R2); (F9) humid separating the obtained non-metallic wastes (RNM) of (R2) to obtain at least one component fraction consisting of plastic wastes (RP), organic cellulosic wastes (Roc) and (R1); (F11) supplying the component fraction of (RP) to at least one thermocatalytic system; (F13) supplying the component fraction of (Roc) to a gasifying system to obtain a synthesis gaseous fuel.    USE - The process is useful for treating solid urban wastes for synthesizing gaseous fuel (claimed), which is useful in combustion engines or cogenerating means for producing electric or thermal energy.    ADVANTAGE - The simple process provides gaseous fuel in an economical manner.    DETAILED DESCRIPTION - Treating solid urban wastes (RSU), comprises: (F1) providing at least one amount of solid urban wastes RSU (R2); (F3) triturating inert wastes (R1) for providing at least one amount of triturated wastes (R2); (F5) separating (R2) from a component of metallic wastes (RM) and (F7) obtaining at least one component of non-metallic wastes (RNM) of (R2); (F9) humid separating (RNM) to obtain at least one component fraction consisting of plastic wastes (RP), organic cellulosic wastes (Roc) and (R1); (F11) supplying the component fraction of (RP) to at least one thermocatalytic system to obtain a combustible mixture; (F13) supplying the component fraction of (Roc) to a gasifying system to obtain a synthesis gaseous fuel. An INDEPENDENT CLAIM is included for a system for treating RSU, preferably adapted for implementing the process, comprises: means for triturating RSU (R1) into (R2); means for separating (R2) into a component of (RM) and a component of (RNM); means for humid separating (RNM) to obtain at least one component fraction of (RP), at least one component fraction of (Roc) and at least one component fraction of (R1); at least one thermocatalytic system adapted to produce a combustible mixture through a thermocatalytic process from the component fraction of (RP); at least one gasifying system adapted to produce a synthesis gaseous fuel (syngas) through a thermo chemical process from the component fraction of (Roc).    DESCRIPTION OF DRAWING(S) - The figure shows a flow diagram of the process treating solid urban wastes for synthesizing gaseous fuel.