Objectives An effective vaccine against SARS-CoV-2 is essential to mitigate the COVID-19 pandemic. In these several months, a number of groups have started to report humoral responses and side effects after BNT162b2 vaccinations. Although these reports demonstrate the safety and efficacy, further studies are warranted to verify these findings. Here we examined the levels of SARS-CoV-2 antibodies in Japanese healthy volunteers who underwent BNT162b2 vaccine, to assess the humoral responses and side effects. Methods Forty-one healthy volunteers’ samples were used for the measurement of SARS-CoV-2 antibodies with chemiluminescent assays against the Receptor Binding Domain (RBD) of the virus. We also measured the side effects of the vaccination. Results Although the levels of IgM varied, all participants were seronegative for IgM and IgG before vaccination, and both IgM and IgG were significantly increased after the vaccinations. We further analyzed the humoral responses in relation to age, and found that the IgG levels for 14 days and 35 days, and IgM levels for 14 days after vaccination showed clear declining trends with age. Commonly reported side effects in the participants were sore arm/pain (90.0%) after the first dose, and generalized weakness/fatigue (70.0%), fever (57.5%), and sore arm/pain (90.0%) after the second dose. Conclusions BNT162b2 vaccination generates sufficient production of IgG especially after the second dose, though the response decreases age-dependently. The high frequencies of generalized weakness/fatigue, fever, and sore arm/pain were not negligible, especially after the second dose. This may be associated with the age characteristics of the population.