The descriptions of the new species Cymbella balkii sp. nov. and C. yerlii sp. nov. were given in this study. The species were found in a karstic limnocrene spring which is one of the most important sources of Sakarya River. Cymbella balkii sp. nov. is very similar to C. pervarians, C. simonsenii, C. percymbiformis, C. perparva, C. alpestris and C. vulgata. Among them, C. pervarians is the most similar taxon however, the former has higher stigmata number and larger valve than the latter. Cymbella yerlii sp. nov. is very similar to C. parva, C. perparva and C. parviformis are similar taxa. Among them, C. parva is the most similar taxon in all related ones with similar outline. However, length/width ratio is higher in C. yerlii than the other taxa.