A new medium for the isolation of Pseudomonas syringae pv. theae was developed. This medium (PST-SM) contains 20g of proteose peptone, 10ml of glycerol, 1.5g of disodium hydrogen phosphate, 1.5g of magnesium sulfate, 250mg of cephalexin, 100mg of cycloheximide and 12g of agar in 1000ml of distilled water, and adjusted to pH 7.2. P. syringae pv. theae produced an opalescent colony, which was distinguishable from most bacteria tested (34 species in 4 genera) when incubated at 25°C from 2 to 4 days. The most characteristic sign of the colony of the wild type strain of P. syringae pv. theae was recognized as a fried-egg type colony with granular and fibril structures when it was irradiated with light in an oblique downward direction from a light microscope at 2 days after incubation. Plating efficiency of this medium to P. syringae pv. theae was the same as King's B medium. P. syringae pv. theae could be detected selectively from infected tea plant tissue with a selective limitation of more than 10² cfu per gram of tissue.