The objective of this work is to investigate some small-celled diatom species and to reconfirm identification of three species of large-celled naviculoid diatoms. Specimens of this investigation were collected from fresh and marine water habitats in Egypt. These specimens were examined using LM and SEM. Seven species of the genus Navicula Bory are described in this study, six of them are belonging to the sub-genus Navicula, while other one (7 ^th) is belonging to the sub genus Minuscula. Full description using LM and SEM, distribution in Egypt, ecological status and comparison between small celled naviculoid diatoms are given. These species are Navicula cryptocephela, N. gregaria, N. viridula, N. heufileri, N. lanceolata, N. pseudoreinharadti and N. luzonensis. This study added a new record to the diatom flora of Egypt and confirm the identification of Pinnularia alpina and two species of Mastogloia.