In an effort to localize the spray-dryer which is markedly used for drying food materials, a experiment was carried out with a wheel type atomizer locally designed and manufactured to evaluate the effect of rotational speed, feed rate and physical properties of liquid food material on the droplet size, and to develop a model to predict the droplet size sprayed at various operational conditions. The result are summarized as follows. 1. The frequency of droplet size sprayed from the atomizer at every treatment were similar to normal distributions. 2. Under the test conditions adopted in this study, that is, rotational speed of the atomizer ranging from 15,000 to 20,000 rpm (55.0 m/sec - 73.3 m/sec), feed rate from 14 to 37 kg/hr and viscosity of the material from 1.14 to 350 cP, the mean volume-surface dia. of droplets was decreased as increase in rotational speed and was not affected significantly by the feed rate and viscosity. 3. Through the dimensional analysis, a prediction model was developed as follows : $$frac{Dvs}{r}=K[frac{Q}{{mu}r}]^a[frac{rN^2}{g}]^b[frac{{ ho}^2r^3g}{{mu}^2}]^c[frac{L}{r}]^d$$ and it was proved that the above model was better in degree of fitness than other models reported. 4. A prediction equation for the droplet size sprayed from the atomizer under the test was expressed as follows : $$frac{Dvs}{r}=0.0215[frac{Q}{{mu}r}]^{0.06}[frac{rN^2}{g}]^{0.3314}[frac{{mu}^2}{{ ho}^2r^3g}]^{0.0158}$$.