Phages of Lactobaciilus casei (PLC) isolated from plant drainage were classified and characterized. The results are as follows : 1. On the basis of host range pattern, phages could be divided into 2 groups (PLC-B and PLC-C). PLC-B group phages could be further divided into 5 sub-groups $(B_1, ;B_2, ;B_3, ;B_4, ;and;B_5)$. Although PLC-C group phages had the same host range, they could be also divided into 2 sub-groups $(C_1;and;C_2)$ by morphlogical type. 2. It was $B_3$ group phages that represented a major proportion (44.4%) of phages tested. However, $B_1$ group phages were shown to have the widest host range. 3. Electron micrographs revealed that the phages fell into three different morphological types. $(B_1, ;B_2, ;and;B_3)$ group phages hd a hexagonal head (52nm in diameter) and a sheathless noncontractile (245 nm in length). $B_4;and;C_2$ group phages had a hexagonal head (56 nm) and a short flexible tail (169nm) having no sheath. $B_5;and;C_1$ group phages were shown to have a hexagonal head (81 nm) and a contractile tail (140 nm) having a sheath, a base plate and tail fibers. 4. The inactivation of the phages by antisera indicated that serological relationships correlated completely with morphological types. 5. $B_1, ;C_1;and;C_2$ group phages produced a large (1, 2 mm in diameter) plaque with a clear ring. The morphology of plaques of $B_3;and;B_5$ group phages was the same as those produced by the above, but the average plaque sizes for $B_3;and;B_5$ were 0.8 mm abd 0.5 mm, respectively. $B_2;and;B_4$ group phages produced a small (0.5 mm) turbid plaque with an irregular edge. 6. The latent period and the average burst size of $B_1;and;B_3$ group phages were 90 min and 100, respectively. These phages reuqired calcium ions for their miltiplication. 7. $B_3$ group phages could not be absrobed to R-variant $KC_1$. 8. The order of resistance of phages to heat was $B_2;>;B_1, B_4;and;B_5;>;B_3;and;C_2, ;B_5$ group phages were more stable than $B_3$ in various pH values. $C_2$ group phages were more sensitive to UV irradiation than $B_1;and;B_3$ group phages. 9. Strains YIT9018 and IAM 1043 were induced by mitomycin C treatment. Phage particles detected in the lysates had a hexagonal head (38 and 49 nm, respectively), but no tail. Any sensitive indicator strain could not be isolated in spite of repaeated trials.