We present the first measurement of the form factor ratios g(1)/f(1) (direc
t axial vector to vector), g(2)/f(1) (second class current), and f(2)/f(1)
(weak magnetism) for the decay Xi (o) --> Sigma (+)e(-)<(<nu>)over bar>(e)
using the KTeV (E799) beam line and detector at Fermilab. From the Sigma () polarization measured with the decay Sigma (+) --> p pi (o) and the e(-)
- <(<nu>)over bar> correlation, we measure g(1)/f(1) to be 1.32 (+0.21)(-0.
17) (stat) +/- 0.05(syst), assuming the SU(3)(f) (flavor) values for g(2)/f
(1) and f(2)/f(1). Our results are all consistent with exact SU(3)(f) symme