We present the first observation of Xi(0) beta decay, using the KTeV beam l
ine and detector at Fermilab. We have identified 176 beta decay events afte
r subtracting a 7 event background. Normalization to 41024 simultaneously c
ollected Xi(0) --> Lambda(0)pi(0) decays yields a branching ratio of Gamma(
Xi(0) --> Sigma(+) e(-)<(nu)over bar>(e))/Gamma(total) = (2.71 +/- 0.22(sta
tistical) +/- 0.31(systematic)) X 10(-4). The flavor symmetric quark model
calculation agrees with this result.