Oxime-type carbamate pesticides having an oxime moiety such as aldicarb, butocarboxim, methomyl, oxamyl, and thiofanox are widely used and have been detected in many fatal cases of accidental exposure or suicide. In forensic toxicology, the accurate determination of blood pesticide concentration is obligatory to prove death by oxime-type carbamate pesticide poisoning. However, the fatal pesticide concentration in blood at autopsy differs from that at the time of death. In this study, we found that oxime-type carbamate pesticides were decomposed by Hb in a temperature-dependent fashion. The mechanism underlying methomyl, aldicarb, oxamyl, and thiofanox decomposition involves the formation of adducts with the amino acids in Hb. With regard to butocarboxim, its decomposition involves the oxidation of the free form and the formation of adducts with the amino acids in Hb. The mass spectra obtained by liquid chromatography quadrupole time-of-flight mass spectrometry revealed that carbamylated amino acid adducts such as Wcar-adduct and Vcar-adduct were formed in Hb solution incubated with methomyl, aldicarb, oxamyl, and thiofanox, whereas alkylated amino acid adducts such as Walkyl-adduct were formed in Hb solution incubated with butocarboxim. These results indicate that aldicarb, butocarboxim, methomyl, oxamyl, and thiofanox are post-mortem changed by Hb.