An efficient microwave-enhanced hydrothermal synthesis strategy was developed for the rapid synthesis of beta-NaGdF4:Ln(3+) (Ln = Yb, Er/Tm/Ho) nanocrystals (NCs) with multicolour upconversion luminescence and paramagnetic properties. It has been found that the uniform beta-NaGdF4:Ln(3+) NCs could be rapidly formed within a few minutes at 160 degrees C and the shape of the NCs can be manipulated from uniform rod-like to spherical just by tuning the initial reactants' concentration. In comparison to conventional hydrothermal routes, a burst homogeneous nucleation and higher growth rate as well as enhanced dimensional homogeneity of the NaGdF4:Ln(3+) was achieved in microwave synthesis. A microwave-heating-based classical crystallization mode and surfactant-assisted anisotropic growth mechanism were proposed for the formation of beta-NaGdF4:Ln(3+) NCs. ; National Basic Research Program of China [2010CB732402]; National Natural Science Foundation of China [30970733, 81171448, 21101130]