Provided are a multi-protocol signal processing apparatus for a next-generation Synchronous Digital Hierarchy (NG-SDH) transponder, and a method thereof. The multi-protocol signal processing apparatus for an NG-SDH transponder, which includes: a sub-signal processing unit for classifying and processing multi-protocol sub-signals based on kinds; an interfacing unit for making interface between the sub-signal processing unit and an optical signal generating unit the same for the multi-protocol sub-signals to use the multi-protocol sub-signals in Synchronous Digital Hierarchy (SDH) flexibly with no regard to the kinds of the multi-protocol sub-signals; and the optical signal generating unit for generating SDH optical signals by aggregating the multi-protocol sub-signals having a predetermined capacity which are transmitted through the interfacing unit into SDH signals, performing framing, and performing optical/electrical (O/E) conversion on the SDH signals in an optical module.