This paper explores the design and fabrication of Micro-Electro-Mechanical capacitors based on vertical carbon nanotube arrays. The devices are realized in vertically single-clamped parallel plate configurations using a dense array of vertically grown MWCNTs on metal lines. The capacitance tuning is performed by electrostatic actuation. From the pull-in voltage value, based on novel analytical model of single-clamped vertical CNT membranes, we extract an equivalent Young modulus of the CNT array ranging in the 10's of MPa. S-parameter measurements combined with an equivalent circuit model enable the demonstration of a capacitors with values of 50-200fF with a tuning range of the order of 19%. ©2009 IEEE.