A stand-alone plasmonic nanocomposite into which a metal nanostructure and an emitting material are integrated is a promising building block for optoelectronics and biophotonics devices. Here we present the plasmonic property of a nanocomposite composed of a Au elongated nanocap and a β-NaYF4 dielectric nanorod. We show that elongation of a Au nanocap results in splitting of the magnetic dipole resonance, and the resonance wavelengths can be controlled in a wide wavelength range by the aspect ratio. As an application of the elongated nanocap, we demonstrate strong enhancement of the near-infrared to visible upconversion of an Er 3+ and Yb 3+ doped β-NaYF4 nanorod by tuning the resonance wavelength of a Au nanocap placed on it to the excitation wavelength.