 The species is intermediate in size for the Akodon boliviensis species group; it is smaller than A. polopi and A. sylvanus, but larger than A. boliviensis and A. caenosus. The more distantly related A. budini and A. simulator, which occur in the same area, are larger. Akodon spegazzinii is variable in coloration, ranging from light to dark and from reddish to yellowish brown. In general, animals in wetter, lower-lying areas are darker, and those in open, dry environments are paler. However, there is also variation within populations, and sometimes young mice are darker and lactating females are more reddish. The formerly recognized species Akodon tucumanensis corresponds to the dark, low-altitude populations, while A. leucolimnaeus and A. alterus represent more reddish, high-altitude animals.
