Abstract:The organic free radicals in anthers were measured by electron spin resonance (ESR) spectroscopy during microspore abortion of male-sterile rice. The test lines were cytoplasmic male-sterile rice(CMSR) V20A, Zhen-shan 97A and Hubei photoperiod sensitive genic malesterile rice(HPGMR) W6154 and Nong-keng 58s. Anthers with different stages of microsporegenesis were vacuum desicated over phosphorus pentoxide then ground in a porcelain mortar. The organic free radicals in the powdered anthers were determined using a JES-Feixg ESR spectrometer and the signal amplitude andg factor were calculated. In all anthers examined, the organic free redical signal showed non-superfine structure with a g factor of 2.0024–2.0031. The levels of organic free radicals were related to the stages of microsporegenesis in both CMSR and HPGMR anthers. At trikaryophase of CMSR V20A and Zhenshan 97A, the signal was approximately 3.2 and 3.8 times stronger than that at dikaryophase, respectively. However, in the maintainance lines of these two CMSR, the changer was only 15–43% from dikaryophase to trikaryophase. The level of organic free radicals in HPGMR anthers, with dikaryophase microspore collected at different fertility transformation under field condition showed a gradual increase. Similar trends of increase were found with the abortion of microspore in anthers of HPGMR W6154s and Nongkeng 58s. Chlorophyll and carotinoid contents in anthers increased with different stages till dikaryophase, then markedly decreased at trikaryophase, which implays that the high ESR signal in abortive stage of microspore was not related to pigments. It is suggested that microspore abortion of male-sterile rice in both CMSR and HPGMR was associated with anomalous free radical metabolism, and its biochemical implication may be somewhat consistent with the aging and senescence process of etber organs.