Monosodium L-glutamate crystals, which are of fragile needle, were obtained by batch crystallization with a natural cooling mode from aqueous solution. The effect of seeding on the product size was examined over a wide range of seed-loadings. The seed-loading ratio C-s defined as the mass ratio of the added seeds to the theoretical yield per batch, had basically the same effect on the product crystal size as ob-served previously in cooling crystallization of mechanically strong granular crystals such as potassium alum. At high seed-loading ratios as C-s greater than or equal to C-s*, where C-s* is a critical value of C-s, seed crystals grew with practically no secondary nucleation. Crystal breakage due to mechanical impacts brought by an agitator occurred only slightly for the small products. For the large crystals the breakage was significant. The breakage also depended on the type of stirrers used; the anchor stirrer induced less breakage than the turbine stirrer. The transient supersaturation was measured on-line by an electro-conductivity method.