Searching for high-performance electrode materials with rapid charge/discharge and high cycling stability is pivotal to broaden the applications of lithium-ion batteries (LIBs). Herein, we report a simple nanochannel-confined synthesis technology of ultrafine Nb2O5 (<10 nm) nanoparticles encapsulated into carbon nanotubes (CNTs) hybrids for LIBs electrode materials. The three crystal forms of Nb2O5 can be respectively obtained simply by changing the temperature of thermal treatment. The ultrafine Nb2O5 nanoparticles dominated by the inner diameter of CNTs expose very high lithiation active sites. The fascinating nanostructure can also possess high structural stability with rapid electron transfer rate. Consequently, the orthorhombic Nb2O5/CNTs hybrids show a maximum specific capacity of 207 mAh g−1 at 0.1 A g−1, which can be maintained 170 mAh g−1 after 1000 cycles. More importantly, a specific capacity of 108 mAh g−1 can still be achieved even at 10 A g−1, much higher than CNTs surface loaded Nb2O5 nanoparticles hybrids. This work provides a channel-space confined synthesis insight for constructing novel electrode materials for high-rate and long-life LIBs.