Increasing the filler content of sheet provides an opportunity for saving production cost through fiber replacement with relatively low-priced filler. But increasing the filler content tends to decrease the strength of paper and filler retention. To overcome these problems, preflocculation technology of fillers has been suggested. To evaluate the effect cationic polymers on the size and size distribution of preflocculated GCC and their shear stability, cationic PAM and cationic starch were used. Results showed that cationic PAM formed large prefloc at low dosage. It was required to add 15 times as high as cationic starch to cationic PAM to obtain the same size prefloc. But preflocs formed with cationic starch was superior in shear stability to those formed with cationic PAM. With the increase of shear rate the size of preflocs decreased. Greater amount of small preflocs or un-flocculated fillers was observed when the dosage of polymers was low and this ended up low ash retention in handsheets.