Background The study of the molecular mechanism of visual plasticity is helpful for the explaining and prevention of strabismus and amblyopia.The effect and significance of NogoA in the strabismus and amblyopia formation are attracting more attention. Objective The present study was to investigate the expression of NogoA in 21a area of visual cortex in strabismic-induced amblyopia cats and explore the possible molecular mechanism of strabismic-induced amblyopia. Methods Sixteen 4-week old clean cats were randomizedly divided into normal group and strabismic-induced amblyopia group and eight for each group.The strabismic-induced amblyopia models were created by cutting off the external rectus in 8 cats.Pattern visual evoked potentials ( P-VEP ) were recorded 1 week after operation and compared with normal cats,and depression of amplitude and prolongation of implied time of P100 wave were as the successful criterion of model.The 200 ml paraformaldehyde was infused via heart to fax the brain under the deep anesthesia and then the cats were sacrificed and the brain cortex sections were prepared.The morphology of 21a zone of cat visual cortex was examined by haematoxylin and eosin staining,and the expressions of NogoA in 21a area of visual cortex were detected by immunohistochemistry with a monoclonal antiNogoA antibody.The use of the animals complied with the Regulations for the Administration of Affair Concerning Experimental Animals by State Science and Technology Commission. Results The implied time and amplitude ratio of VEP P100 wave were (98.10±7.07)ms and (0.83±0.14) in normal group,and those in strabismic-induced amblyopia group were (108.50±6.95 )ms and (0.35 ±0.09 ),showing significant differences between two groups (t=4.450,P=0.005 ; t =5.970,P =0.005 ).The numbers of neurons were similar in 21a area of visual cortex between the two groups,but the volume of the neurons was lessen in strabismic-induced amblyopia group.The positive cell densities for NogoA were ( 387.37±2.01 ) cells/mm2,( 354.58± 1.85 ) cells/mm2 and ( 289.68± 1.81 ) cells/mm2 in layer Ⅱ/Ⅲ,Ⅳ and V/V[ respectively in strabismic-induced amblyopia group,and those in normal group were ( 161.39± 1.98 ) cells/mm2,( 128.93 ± 1.26 ) cells/mm2 and ( 96.25 ± 1.49 ) cells/mm2,indicating a significant increase in model cats ( t =- 160.400,- 201.890,- 164.740,P =0.000 ). Conclusions NogoA may play an important role in the regulation of the sensitive developmental period of visual sense and its plasticity.