A quenching apparatus for a reactor is disclosed. The quenching apparatus includes a quenching unit (31) and a mixing unit (41). The quenching unit includes fluid distribution pipes (33) which branch off from a central portion of the quenching unit in radial directions and eject quenching fluid, and one or more first fluid outlets (35) which are formed through the bottom of the quenching unit. The mixing unit includes inclined baffles (43), one or more partitions (42) and a second fluid outlet (45). The inclined baffles are respectively disposed under the first fluid outlets. The partitions partition a space between inner and outer sidewalls of the mixing unit into a plurality of separated spaces in which the inclined baffles are respectively disposed. Fluid guided by the inclined baffles and the partitions is discharged out of the mixing unit through the second fluid outlet.