The routine use of electron microscopy (EM) techniques in diatom research resulted in fast progress in understanding the ultrastructure and construction of diatoms. However, both scanning (SEM) and transmission electron microscopy (TEM) did not allow to cutting through the diatom sili- ceous exoskeleton on demand. To illustrate a speci c part of the frustule, valve, mantle or girdle was always a matter of good luck and nding a broken exoskeleton at the right site and right angle. is problem is now solved by use of a modern tool, Focused Ion Beam (FIB), developed in mate- rial and nanosciences research. Use of FIB in diatom research dates to the early 21st Century and is increasingly becoming a routine tool. FIB can be used as a nanomanipulation and nanopreparation method technique which allows nanocuts of diatom frustules at any site within the frustule with desired orientation at any magni cation. Presented in this paper are results of FIB use in studies of the ultrastructure of selected diatoms. In particular, bene ts of FIB application are shown in studies on valves with higher degrees of complication due to their complex stria structure, e.g., character- ized by the presence of chambers.