Discharge nozzle (10) for continuous casting of slabs having narrow sides between about 30 and about 300 mm. wide, which is employed to distribute liquid metal in a continuous casting mould and is of a type comprising a substantially vertical discharge pipe (11), which is closed at its lower end and includes lateral terminal discharge holes (14) facing towards the narrow sides of the mould and cooperating with means (13) that distribute and deflect the flow of liquid metal, the discharge pipe (11) comprising a first segment (11a) having a downwardly converging circular cross-section and a second downwardly diverging segment (11b) with a cross-section which can be varied progressively from circular to substantially rectangular at least with rounded short sides, the distribution and deflection means (13) consisting of two distribution chambers (15), one per each lateral discharge hole (14), the chambers (15) being open at their upper (16a) and lower (16b) portions and being defined by a sidewall (17) which, at the opposite side of the lateral discharge hole (14), is conformed as a downwardly diverging deflector (18) forming an angle ".alpha." with the vertical between 10.degree. and 35.degree., the lateral discharge holes (14) being adjacent to a bottom end wall (12) and having an overall section about equal to the section of the outlet of the second segment (11b) of the discharge pipe (11), each distribution chamber (15) defining an upper discharge outlet (16a) and a lower discharge outlet (16b).