We have discovered chemiluminescence upon the thermal decomposition of acetylcyclohexanesulfonyl peroxide (SP) in the absence of oxygen. SP was synthesized according to the procedure of Graf [i]. The reaction was carried out in a glass reactor at 50~ in a solution of decane and cyclohexane ([cyclo-C6HIIS(O2)OOC(O)CH3]0 = 0.03-0.1 mole/liter). The chemiluminescence intensity (I) was measured using an FEU-II9 photomultiplier. A set of standard light filters (USSR State Standard GOST 9411-81) was used to study the spectral composition of the irradiation. The solution of SP was placed in a reactor thoroughly flushed by argon, purified to remove oxygen ([02] < 1.10 -5 mole/liter) using a PG instrument (TU-25-II-I001-75), and brought to constant temperature over 4-5 min. Chemiluminescence was observed and I decreased according to the consumption of SP. The chemiluminescence at 500-700 nm contains a clear maximum at 580-600 nm and two weaker signals with maxima in the vicinity of 650 and 690 nm. The addition of an alkyl radical trap to the solution of SP, namely, 2,2,6,6-tetramethyl-4-hydroxypyridine 1-oxide (5-10 -4 mole/liter) or 1,4-benzoquinone (9-10 -4 mole/liter) leads to a fivefold reduction in I. Apparently, the emitter is formed in reactions involving alkyl radicals. When air is bubbled through the solution of SP, chemiluminescence appears at short wavelengths (maxima at 400-440 and 500-540 run), while the long-wavelength emission is diminished. Analogous chemiluminescence is observed at 400-540 run upon the decomposition of dicyclohexyl peroxydicarbonate under the same conditions. The short-wavelength part of the chemiluminescence spectrum observed upon the decomposition of SP in the presence of 02 is probably a consequence of radiative deactivation of excited carbonyl compounds (cyclohexanone, decanones, and formaldehyde) formed upon recombination of the corresponding peroxyl radicals.