In order to simplify the management of certificates and keys, improve the computation efficiency and the security of the certificateless signcryption scheme at the same time, Chen Hong, et al. proposed a certificate- less signcryption scheme of verifiable security without pairing and claimed that their scheme satisfied confiden- tiality and unforgeability in the random oracle model. Unfortunately, by constructing three types of attacks, the study indicated that Chen Hong’s et al. certificateless signcryption scheme could not resist the public-key sub- stitute attack, the master key and partial private key exposures attack, and the collusion attack. Finally, the causes of the vulnerabilities were analyzed, and the improved scheme was proposed.