Theory of spontaneous symmetry breaking is analyzed in terms of quaternions
. Lagrangian density is written as a scalar quantity of quaternionic valued
Function. For minimizing the potential V (phi) = mu (2)<(<phi>)over bar>ph
i+lambda(<(<phi>)over bar>phi)(2) the vacuum expectations values <(<nu>)ove
r bar>nu = -mu (2)/2 lambda are obtained in a consistent way. Quaternion va
lued scalar lagrangian reduces four different field equations associated wi
th scalar fields phi (0), phi (1), phi (2) and phi (3) of a quaternion phi
= phi (0) + e(1)phi (1) + e(2)phi (2) + e(3)phi (3). Spontaneous breaking o
f global and local gauge symmetries are analyzed by means of quaternions. I
t is shown that the quaternion gauge group SO(4) is spontaneously broken to
SO(4) approximate to SO(3) x SO(3) associated with two gauge field quantas
. Quaternionic gauge theory is investigated as the composite stales of quar
ks and leptons associated with vector and scaler part of quaternion valued
fields, respectively. Weinberg-Salam SU(2) x U(1) gauge theory of electrowe
ak interaction is extensively studied to enlarge the gauge group SU(2)(L) x
SU(2)(R) x U(1).