Greater dissimilarity is encountered with respect to Proto-Sinitic. The contrast of aspirated and unaspirated voiceless stops in initial position is most likely the result of lost initial cluster elements as in Proto-Tibeto-Burman. The voiced stops possibly also had the aspirated–unaspirated distinction. Unlike Tibeto-Burman, two series of stops in syllable final position are posited for Old Chinese, but it is not clear if the contrast involved voicing or other features. One series is in general without an exact correspondence in Tibeto-Burman languages, but Burmish Maru has final stops in a number of these words. Similar isolated cases are found in Tibetan and in Tai.

Old Chinese has two more relevant points of articulation, or sound-producing positions of the mouth, than Proto-Tibeto-Burman: palatal (in which the tongue blade touches the palate) and retroflex (in which the tip of the tongue is curled upward toward the palate). But these two types of sounds may be explained as the result of influence from lost Proto-Sinitic medial sounds (a palatal -y- and a retroflex -r-). The relationship between these specific medial sounds and similar elements in Tibeto-Karen is, however, not certain. Dental affricate sounds in Old Chinese, which begin as stops with complete stoppage of the breath stream and conclude as fricatives with incomplete air stoppage and audible friction, can at least be explained partly as metathesized (transposed) forms of prefix s- plus a dental sound in Proto-Sinitic (e.g., st changes to ts). Old Chinese possessed initial consonant clusters containing -l- as a second element, so Proto-Sinitic can reasonably be supposed to have had the same three medial elements as Proto-Tibeto-Burman: -y-, -l-, and -r-. There are few, if any, traces in Old Chinese of the more complicated clusters and the minor syllables of Tibeto-Burman.

The vowel system of Old Chinese as reconstructed (1940) by the linguist Bernhard Karlgren to account especially for the language of the Shijing, an anthology of Chinese poetry compiled in the 6th–5th centuries bce, seems surprisingly complicated as compared to that of Proto-Tibeto-Burman. Probably some of the vowels can be explained as diphthongs or as combinations of vowels plus specific classes of consonants (e.g., labialized, retroflex, palatal).

As in Karen and Burmese-Loloish, the tones of Sinitic can be reduced to two (with some syllables or syllabic types being neutral or unaffected by the tonal system; the modern Sinitic languages have from two to as many as eight or nine tones). Monosyllabicity of roots and morphological affixation were characteristic features of Proto-Sino-Tibetan as they were of Proto-Tibeto-Karen.