The samples of 25 nL of chloride and cyanide were determined with a kind of glass capillary indicating electrodes by potentiometry. Silver was deposited by the silver-mirror reaction on the inner surface of the glass capillary with a volume of 25 nL. The AgCl film and the AgI film were formed by the treatment of the capillary with a FeCl3 solution and further with a KI solution. The samples were collected automatically into the capillary by the capillary ascension. The procedure in the measurement was merely to place a reference electrode and a capillary indicating electrode vertically on a strip filter paper containing a 0.1 mol/L NaNO3 solution. The various i.d. of the capillary electrodes were used to determine samples ranging from 25 nL to dozens of microliters. The ranges of the linear response to chloride and cyanide were 3.2×10-4-2.2×10-1 mol/L and 1.0×10-5-1.0×10-1 mol/L with an average slope of 55.2 and 52-62 mV/decade, respectively. The samples with various concentrations of chloride and cyanide were determined, and the relative standard deviations were less than 7%.