This paper is focused on an evaluation of quality of synthesized sign speech and a comparison of sign and visual speech. The evaluation has been performed with the Czech sign speech synthesis system. The system produces a manual component as well as a non-manual component given by the lip articulation. The perception test by deaf children from primary school is scored on the isolated signs. Two studies are designed for 5-6 and 11-13 years old pupils. It uses the multiple-choice test composed from picture of the signs to get an intelligibility score. The results confirm intelligibility of the synthesized sign speech as well as visual speech and indicate also statistically a significant difference between perception of sign and visual speech.