The effect of five constant relative humidity (RH) regimes (12, 33, 55, 75, and 94%) on ovarian maturation, adult longevity, and egg production of Bactrocera (Dacus) oleae (Gmelin) (Diptera: Tephritidae) was studied at 25 ± 1°C and a photoperiod of 16:8 (L:D) h under laboratory conditions. The experimental insects developed in the preimaginal stages at 16:8 (L:D) h and 25 ± 1°C, and the adults were maintained in plastic cages in sealed plastic containers with saturated water salt solutions in their base to control RH. In the experiments concerning longevity and egg production, the adults were maintained individually, whereas in those concerning ovarian maturation they were in groups of 10 females and 10 males. Ovarian maturation was much reduced and the number of mature oocytes in the ovaries was very low in 7-d-old females maintained at 12 and 33% RH. By contrast, a high percentage of females of that age maintained at 55, 75, and 94% RHs had mature oocytes in their ovaries. Longevity of adult females, egg production and egg hatch were low at 12% RH. They were significantly higher at 33% RH, and even more so at 55 and 75% RHs but declined at 94% RH. These results could be useful for the mass rearing of B. oleae and for better understanding its population dynamics under field conditions.