Recently, Hou et al. Proposed an improved certificate less aggregate signature (CLASS) scheme based on Xiong et al's scheme. They also demonstrated the scheme is provably secure in the random oracle model. Unfortunately, by giving concrete attacks, we point out that Hou et al.'s scheme is not secure in their security model. Then, we propose an improved certificate less signature (CLS) scheme and use it to construct an improved certificate less aggregate signature (CLAS) scheme.