3-Hydroxypyridazine 1-oxide (I) and its methyl homologs (II), (III), and (IV) were submitted to electrophilic substitutions such as nitration and halogenation. Due to the additional polar effect of both N-oxide and hydroxyl groups, introduction of nitro group and halogen in 4-and/or 6-positions was successfully concluded. By heating with potassium hydrosulfide, nucleophilic substitution of the brominated compounds (XXXI and XXXVI) was also carried out, affording mercapto compounds (XXXII and XXXVII).