  We study the (p,q)5-brane dynamics from the viewpoint of Matrix string theory
in the T-dualized ALE background. The most remarkable feature in the
(p,q)5-brane is the existence of ``fractional string'', which appears as the
instanton of 5-brane gauge theory. We approach to the physical aspects of
fractional string by means of the two types of Matrix string probes: One of
which is that given in hep-th/9710065. As the second probe we present the
Matrix string theory describing the fractional string itself. We calculate the
moduli space metrics in the respective cases and argue on the specific
behaviors of fractional string. Especially, we show that the ``joining''
process of fractional strings can be realized as the transition from the
Coulomb branch to the Higgs branch of the fractional string probe. In this
argument, we emphasize the importance of some monodromies related with the
theta-angle of the 5-brane gauge theory.
