As a newly discovered class of radio-loud active galactic nuclei (AGNs), the gamma-ray detected narrow-line Seyfert 1 galaxies (NLS1s) launch powerful jets which are generally found only in blazars and radio galaxies. However, their black hole (BH) masses as estimated from the broad emission lines are one order of magnitude or more lower than those in blazars. This brings new challenges for explaining the radio loudness triggering in AGNs. It is still under debate whether their BH masses from the commonly used virial method are underestimated. Here we present an estimate of the BH mass for the gamma-ray detected NLS1 1H 0323+342, an archetype of this class, from the X-ray variability which is inclination independent. Our results independently confirm that this gamma-ray detected NLS1 harbors a $(2.8-7.9)times10^6,M_{odot}$ BH similar to those in normal NLS1s rather than those in blazars.
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