High sulfur coal sample from C1 seam in Tabas mine (Iran) was studied. The effect of microwave pre-irradiation followed by a peroxyacetic acid (PAA) desulfurization on sulfur forms was investigated by atmospheric pressure-temperature-programmed reduction (AP-TPR) method. Implementing microwave irradiation at 300 W for 2 min resulted in a maximum total sulfur and organic sulfur reduction by PAA of about 63% and 49%, respectively. Pyrite reduction in the microwave treated - PAA desulfurized samples is more than 84% on all studied samples. Pre-irradiation improved pyrite removal by PAA around 21%. Organic sulfur alteration after PAA desulfurization was discussed based on recorded m/z 34 (H2S+) AP-TPR profile changes, qualitatively and partly quantitatively. Based on the m/z 48 and 64 (SO+, SO2+) AP-TPR profiles, organic sulfate and also minor amounts of sulfones and sulfoxides in the PAA treated samples have been noticed. AP-TPR off-line coupled with TD-GC/MS gives additional proves of the formation of oxidized sulfur compound present by PAA desulfurization and for a de-methylation reaction mechanism because of the pre-irradiation treatment. (C) 2015 Elsevier Ltd. All rights reserved.