Bacillariophycean algae are unicellular or colonial forms in freshwater plankton and also lived as epiphyte on other algae and higher plants in Gajner lake. They form a large proportion of bottom flora of lake. We were collected algal samples twice a month from January,2017-December,2017. Our study deals with periodicity and taxonomy of newely reported Bacillariophycean taxa of Gajner lake, which is a fresh water body of Bikaner district. In our present investigation floristic composition, periodicity and seasonal variations were observed throughout the year. There are 25 species of 13 genera of Bacillariophycean taxa were reported. These diatoms showed remarkable seasonal variations in numbers, species and density.