The liquid flame spray technique for nanoparticle production was investigated by in situ droplet and particle diagnostics with and without spray combustion in the presence or absence of zirconia particle precursor. In particular, the effect of atomization gas flow and liquid feed rates on spray characteristics and particle morphology was studied. Droplet size distributions were determined from submicron to supermicron range using phase Doppler anemometry (PDA, droplets >1 mu m), scanning mobility particle sizer (droplets <1 mu m), and electrical low-pressure impactor (whole droplet size range). The number mean droplet diameters were submicron, while the mass mean diameters were in the supermicron range. During spray combustion, droplet size distributions measured by PDA were affected by fast droplet evaporation and combustion such that an increasing atomization gas flow rate led to decreasing Sauter mean diameters. Average downstream gas velocities estimated by PDA decreased for increasing liquid feed and constant atomization gas flow. Also, particle production, that is, precursor feed to the flame, reduced the gas velocities. Zirconia product composition and morphology were determined by transmission electron microscopy and X-ray diffraction. High atomization gas flow rates resulted in complete precursor evaporation and produced zirconia particles of uniform size and shape.