  Solar microwave type III pair burst is composed of normal and reverse-sloped
(RS) burst branches with oppositely fast frequency drifts. It is the most
sensitive signature of the primary energy release and electron accelerations in
flares. This work reported 11 microwave type III pair events in 9 flares
observed by radio spectrometers in China and the Czech Republic at frequency of
0.80 - 7.60 GHz during 1994 - 2014. These type III pairs occurred in flare
impulsive and postflare phases with separate frequency in range of 1.08 - 3.42
GHz and frequency gap 10 - 1700 MHz. The frequency drift increases with the
separate frequency (f_{x}), the lifetime of each burst is anti-correlated to
f_{x}, while the frequency gap is independent to f_{x}. In most events, the
normal branches are drifting obviously faster than the RS branches. The type
III pairs occurring in flare impulsive phase have lower separate frequency,
longer lifetime, wider frequency gap, and slower frequency drift than that
occurring in postflare phase. And the latter always has strong circular
polarization. Further analysis indicates that near the flare energy-release
sites the plasma density is about 10^{10} - 10^{11},cm^{-3} and temperature
higher than 10^{7} K . These results provide new constraints to the
acceleration mechanism in solar flares.
