a b s t r a c t The perinuclear theca (PT) is a cytoskeletal structure that surrounds the mammal sperm nucleus which must be disrupted once the sperm has penetrated the oocyte to permit normal chromatin decondensa-tion and formation of male pronucleus. F-actin is a thermo sensitive protein found in the equatorial segment which is involved in the stability of PT. It has been reported that cryopreservation induces alter-ations in nuclear decondensation of spermatozoa, which have been interpreted as an over condensation. The aims of the present study were identified the presence of changes in sperm sPT integrity of frozen– thawed boar spermatozoa and its effect in sperm nuclei decondensation; and whether changes in the actin cytoskeleton are involved using an in vitro model to test probably differences in a chemical decondensation (DTT/heparin) between fresh (FS) and frozen–thawed (TS) spermatozoa. Results showed an increase on sPT damage in TS (P < 0.001), and significant changes in sperm chromatin nuclear decondensation (P < 0.05). In same way differences on the swelling degree was found assessed by measures in equatorial region of head sperm (P < 0.05). Evaluation with rodamine-labeled actin (0.2 lM) showed two different patterns with differences in percentages before and after cryopreservation (P < 0.001). F-actin stabilization constrained the equatorial segment of FS while this was not observed in TS. The data showed that the presence of early changes in sPT integrity and changes in the F-actin localization on TS may suggest the participation in F-actin in decondensation process and probably that the disruption of actin-PT interaction during freez-ing–thawing process could have far-reaching consequences for the subsequent fertility of spermatozoa.