Nicardipine hydrochloride injection, a dihydropyridine calcium channel blocker, is an acidic drug. The package insert recommends that nicardipine injection should be administered at the concentrations of 0.01-0.02%. However, the drug often induces venous irritation despite infusion at the recommended concentrations in the intensive care unit (ICU) at Kyushu University Hospital. Therefore, we retrospectively investigated the incidence and risk factors of venous irritation in ICU patients. Univariate and multivariate analyses revealed that the administration time and infusion rate of the drug were significantly related to venous irritation (<i>P</i><0.05). Patients who were infused with nicardipine injection (administration time: more than 24 h, infusion rate: more than 45 mL/h) developed the venous irritation frequently (7 of 9, 77.8%). In the case of infusion of nicardipine injection for more than 96 h, the patients experience severe vascular damage and needed for treatment with medicine such as topical steroids. These results suggest that the administration time and infusion rate are involved in nicardipine injection-induced venous irritation, and it is necessary to pay attention to these factors as well as observing the instructions in the package insert.