Abstract: Some behavioural characteristics of Lysiphlebus fabarum (Marshall) as an important parasitoid of Aphis fabae was studied under laboratory conditions (21±1°C, a relative humidity of 70±5% and a photoperiod of 14:10 L:D h.) using different stages of Aphis fabae and its host plant. In this study, mating behaviour, sequences of oviposition, time spent for an adult parasitoid to emerge from its mummified aphid host and the effect of temperature and relative humidity on the percentage of adult emergence were determined. Average mating and oviposition handling times lasted 37.1±2.8 and 77.2±3.8 sec, respectively. It took 19.8±1.19 min for an adult wasp to emerge from its mummified aphid host. Females oviposited on or between sternal segments of aphid host thorax, usually on second or third segments. The time intervals between ovipostion to mummification and to the emergence of adult parasitoids were inversely dependent on host stages and decreased as the aphid nymphs grew to adult stage. The time interval between mummification and adult emergence decreased as the temperature increased. Results showed that temperature and relative humidity influenced percentage of adult emergence. Highest percentage was observed at 25°C and the lowest at 30°C with 50±5% of relative humidity, while the highest and lowest percentage of adult emergence was observed at 15°C and 30°C with RH of 70±5%, respectively.