In Erzya- and Moksha-Mordvin, vowel and consonant durations are not phonologically distinctive. There is, however, a morphophonologically conditioned difference between single consonants and secondary geminates that occurs at morpheme boundaries: E kańńems, M kańńǝms (kand-o-ms, kand-ǝ-ms ’to carry’ + -ń- of the frequentative suffix). This article focuses on the durational relationship between geminates and singletons in Moksha. The material includes also word-internal intervocalic consonants, among them voiceless plosive and fricative singletons that allegedly lengthen in this position and sound as geminate-like segments. The results show that geminates are twice as long as singletons, including voiceless plosives and fricatives, and relative duration between geminates and singletons is segment-inherent (1.8 for voiceless and 2.1 for voiced consonants). The geminates, compared to the singletons, produced a more salient shortening effect on the preceding vowels. The collected data are necessary for defining the vowel-consonant durational relationship within prosodic units. An extensive analysis of gemination in Erzya and Moksha would be useful for a future investigation of morphophonological changes in the ­Mordvin languages.