Objective To explore the effect of cryopreserved canine kidney cells (MDCK)single -layer on the isolation and proliferation of influenza virus B.Methods Revived P17 MDCK cells were passage for 2 -4 gener-ations,and subsequently preserved in 4℃ refrigerator for 3,6 and 9 days,respectively.Under same experimental con-ditions,the 4℃ refigerater preserved cells were co -incubated with influenza -like illness(ILI)throat swab speci-mens.Cytopathic effect (CPE)was observed,and the proliferation of virus was determined using real -time PCR and the hemagglutinin titers were determined by serological test.Results (1)CPE:The CPE of the MDCK cells pre-served in 4℃ refrigerator for 3 or 6 days had no significant differences compared with that in the control group,while the cell preserved in 4℃ refrigerator for 9 days showed CPE fastly and maintained for a short time.(2)Real -time PCR:the proliferation of influenza virus B in the MDCK cells preserved with 4℃refrigerator for 3 or 6 days (25.86 × 105 -30.25 ×106 ,26.31 ×105 -30.54 ×106 )had on difference compared with that of the control group (24.82 × 105 -29.86 ×106 ),with the proliferation rate of 105 to 106 times,while the proliferation cell with 4℃ cryopreserved for 9 days(19.72 ×104 -28.34 ×105 )the proliferation in cells preserved for 9 days was sharply decreased,with pro-liferation rate of 104 to 105 times.(3)The HA titer:The virus strains with hemagglutination titer above or equal to 116 (P >0.05)isolated with MDCK cells preserved in 4℃ refrigerator 3 or 6 days were not significantly different from that of the control group (10.92 ±0.79).And the cells with 4℃ cryopreserved for 9 days were significantly dicreased (P <0.01).Conclusion No significant effects on the isolation and proliferation of influenza virus B using MDCK cell preserved in 4℃ frigerator for near one week were observed in the present study.