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We present Hubble Space Telescope\/ observations of 4 globular clusters in M31, which cover a wide range of metallicity. These observations were made using the F555W ($V$) and F814W ($I$) filters with WFPC-2, and the exposure times were 2000~s in each filter. We display color-magnitude diagrams of the four clusters. The depth of these observations is about 1~mag fainter than the horizontal branches of the clusters, allowing easy identification of the horizontal branches. The horizontal branch morphologies change from blue to red with increasing metallicity as expected from Galactic globular clusters. We also discuss the implications of these observations on the calibration of absolute magnitudes of RR Lyrae stars and the distance to M31.
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