  IRAS 19312+1950 is a unique SiO maser source, exhibiting a rich set of
molecular radio lines, although SiO maser sources are usually identified as
oxygen-rich evolved stars, in which chemistry is relatively simple comparing
with carbon-rich environments. The rich chemistry of IRAS 19312+1950 has raised
a problem in circumstellar chemistry if this object is really an oxygen-rich
evolved star, but its evolutional status is still controversial. In this paper,
we briefly review the previous observations of IRAS 19312+1950, as well as
presenting preliminary results of recent VLBI observations in maser lines.
