The title compound, 2tertbutyl5(4tertbutylbenzylthio)4chloropyridazin3(2H)one, was synthesized from 1tertbutylhydrazine, (%Z%)2,3dichloro3formylacrylic acid and (4tertbutylphenyl)methanethiol in several steps. It crystallized in an orthorhombic space group Pnma with M%_r=364.93(C_ 19 H_ 25 ClN_2OS), a=1.0091(2) nm, b=0.7076(2) nm, c=2.8103(5) nm, V=2.0066(6) nm+3, Z=4, D%_c=1.192 g/cm~ 3 , F(000)=765, μ=0.301 mm~ -1 , final R_1=0.0665, and wR=0.1913 for 1927 unique reflections. Inter and intramolecular hydrogen bond C_H…O interactions stabilize the structure. The title compound, 2tertbutyl5 (4tertbutylbenzylthio) 4chloropyridazin3 (2H) one, was synthesized from 1tertbutylhydrazine, (% Z%) 2,3dichloro It crystallized in an orthorhombic space group Pnma with M% _r = 364.93 (C_19H_25ClN_2OS), a = 1.0091 (2) nm, b = 0.7076 (2) nm, c = 2.8103 (5) nm, V = 2.0066 (6) nm + 3, Z = 4, D% _c = 1.192 g / cm ~ 3, F ~ -1, final R_1 = 0.0665, and wR = 0.1913 for 1927 unique reflections. Inter and intramolecular hydrogen bond C_H ... O interactions stabilize the structure.