We previously reported that a rotationally reciprocating impeller, which slowly rotates back and forth with a sinusoidal change in the rotational speed, can realize superior mixing performance even under moderate fluid flow. In the case of crystallization process, it is expected that the rotationally reciprocating mixing suppresses crystal brakeage caused by collision to impeller plate and inhomogeneous supersaturation due to notable mixing performance. In the present study, we studied reactive crystallization process of salicylic acid and investigated the effect of mixing conditions on the size and shape of crystals. For a steady rotational mixing, the largest crystal size was obtained at the appropriate mixing condition, and the size and shape of crystals are both affected by the rotational speed. Meanwhile, it is found that the size of crystals maintained roughly constant in the wide range of mixing condition of the rotationally reciprocating mixing. Additionally, no significant difference in the shape was observed even at different reciprocating conditions.