Flame synthesis was applied to produce metal oxide nanoparticles such as titanium dioxide ($TiO_2$) and lithium manganese oxide ($LiMn2_O_4$) from sprayed droplets of precursor solution. A high enough flame temperature was used for the complete thermal decomposition of the aerosol precursor. Molar concentration of the precursor solution and the flow rate of combustion gas such as hydrogen were varied to control the particle size, the size distribution and the crystal structure. Crystalline $TiO_2$ and $LiMn_2O_4$ nanoparticles with the average particle diameter ranging from 9 to 45 nm and from 12 to 19nm were synthesized, respectively.