Hafnium tetrachloride is one of the most commonly used precursors for atomic layer deposition of HfO2. According to the experimental result, chlorine residue is almost unavoidably incorporated during the deposition process. We performed first-principles calculation to study the effects of chlorine residue in HfO2 and found that chlorine at the interstitial site serves as a source of negative fixed charge while chlorine at the oxygen substitutional site changes its charge state depending on the position of the electron chemical potential within the band gap of HfO2. Moreover, chlorine also reduces the band gap of HfO2 by raising the valence band maximum.