This paper addresses the problem of low-power fanout optimization with multiple threshold voltage inverters. Introducing splitting and merging conversions that preserve delay, power, and input capacitance, the fanout tree is converted to a set of inverter chains and for each chain the optimal sizes and threshold voltages are determined. Experimental results show that using this technique, the power dissipation of fanout tree is reduced by an average of 33% for a state-of-the-art CMOS technology. Categories and Subject Descriptors B.6.3 [Design Aids]: Automatic synthesis, Optimization. General Terms Algorithms, Design, Performance. Keywords Low-power design, Fanout optimization, Fanout tree, Buffer chain.