The major toxicities associated with paclitaxel(PTX)-based chemotherapy are myelosuppression, peripheral neuropathy and myalgia/arthralgia. In the present study, a retrospective study was carried out to compare the incidence of adverse events during PTX-based chemotherapy between 58 cases treated every 3 weeks(tri-weekly regimen)for breast cancer and non-small cell lung cancer and 47 cases with weekly regimen for breast cancer and gastric cancer. Hematological toxicity such as neutropenia and thrombocytopenia, peripheral neuropathy and myalgia/arthralgia occurred more frequently in patients with a tri-weekly regimen than in those with a weekly regimen(grade 3/4 neutropenia: 65.5% versus 12.8%, odds ratio; 12.98, grade 2/3 peripheral neuropathy: 24.1% versus 6.4%, odds ratio; 4.67, and grade 2/3 myalgia/arthralgia: 43.1% versus 4.3%, odds ratio; 17.05). The development of peripheral neuropathy and myalgia/arthralgia was dependent on the dose per injection, but not on the cumulative dose of PTX. The initial onset of peripheral neuropathy and myalgia/arthralgia was observed in more than 80% of patients during the first course of the tri-weekly regimen, while it was seen in any course of the weekly regimen. The incidence of other nonhematological adverse events was not different between the two regimens except for nausea. Our present findings suggest that the peripheral neuropathy and myalgia/arthralgia are highly frequent adverse events that depend on the dose per injection of PTX, in which the incidence was more frequent in the tri-weekly than in the weekly regimen.