Some behavioural characteristics of Lysiphlebus fabarum (Marshall) as an important parasitoid of Aphis fabae was studied under laboratory conditions (21[plus or minus]1[degree]C, a relative humidity of 70[plus or minus]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[plus or minus]2.8 and 77.2[plus or minus]3.8 sec, respectively. It took 19.8[plus or minus]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 Sage. 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[degree]C and the lowest at 30[degree]C with 50[plus or minus]5% of relative humidity, while the highest and lowest percentage of adult emergence was observed at 15[degree]C and 30[degree]C with RH of 70[plus or minus]5%, respectively. Lysiphlebus fabarum (Aphidiidae) : Parasite Aphis fabae (Aphidoidea) : Host Reproduction; Life cycle and development; Development; Metamorphosis; Parasites diseases and disorders; Parasites; Insect parasites; Hosts; Insect hosts; Abiotic factors; Physical factors Aphis fabae; Hymenopteran parasites; Host parasite relations; parasite reproduction & humidity & temperature effect on emergence; Lysiphlebus fabarum; Humidity; Temperature Lysiphlebus fabarum; Reproductive behaviour; Emergence; Hemipteran hosts; Host parasite relations; reproductive behaviour & humidity & temperature effect on emergence; Aphis fabae; Humidity; Temperature none