This paper considers the robust stability of the interconnection of a linear time-invariant differential nominal system and passive uncertainties in the behavioral framework. A generalized version of the well-known passivity theorem is formulated by using quadratic differential forms. Based on the generalized passivity theorem, it is proved that, if the nominal system is ¦µ-passive, the interconnection is robustly stable against
strictly (-¦µ)-passive uncertainty. Moreover, we show that the ¦µ-passivity of the nominal system is a necessary and sufficient condition for the robust stability with regularity constraint of the uncertain interconnection.