In Khalkha Mongolian, there are two contrastive series of obstruents. Recent acoustic analyses have revealed that this contrast is based on aspiration. Some previous studies have reported that aspiration is realized as postaspiration in word-initial position and as preaspiration in word-medial and final positions. Preaspiration is said to be characterized as clearly audible aspiration noise and at least partial devoicing of the preceding segment. However, almost all the data used in the previous studies are for obstruents preceded by a short vowel; acoustic data of obstruents preceded by other segments are lacking. This paper examines the acoustic realization of word-medial aspirated obstruents preceded by a short vowel, a long vowel, and a nasal consonant in Khalkha Mongolian. Aproduction experiment and acoustic analyses indicate that preaspiration in Khalkha Mongolian appears in various forms according to the phonological environment:When an aspirated obstruent is preceded by a short vowel, preaspiration is realized as breathy voicing and/or devoicingon the vowel, whereas in the case of long vowels before an aspirated obstruent, it is mainly realized as partial breathy voice on the vowel,which is rarely devoiced. When the preceding segment is a nasal consonant, preaspiration is not salient in many cases. Instead, aspirated obstruents are characterized as being preceded by shorter nasals and having longer stop closures than their unaspirated counterparts.