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We succeeded in obtaining gas discharge in 250-, 150-, and 50-mum inner-diameter (i.d.) hollow-core fibers (HCFs) by using longitudinal direct current excitation. Stable glow discharges of at least several minutes were observed for these HCFs. A flash glow was also observed for an HCF with an i.d. of ~20 mum. Breakdown of helium and argon gases in a 26.2-cm-long 250-mum-i.d. HCF was achieved with a voltage of less than 30 kV. Breakdown voltages of helium and argon gases were measured for various bore sizes, fiber lengths, and a pressure range from below 1 to 50 Torr. Experimental results deviated from previous theoretical models and further theoretical and experimental investigations are needed to understand the unique characteristics of gas-discharge in HCFs with i.d. below 250 mum.