Investigations were carried out on "Bionomics of fruit fly, Bectrocera cucurbitae (Coquillet) on cucumber under laboratory condition" at Department of Entomology, College of Agriculture, Junagadh Agricultural University, Junagadh during kharif-2015 on cucumber variety dharwad green. Observations on various life stages were made at a 17.7 0 C to 33.4 0 C temperature (Av. 26.87 0C ± 5.66) and 57.8 to 89.7 per cent relative humidity (Av. 81.54 ± 6.67 % RH). The eggs were laid in the fruit tissues. The average incubation period was found to be 19.6 ± 4.72 hours. The average length and width of egg 1.12 ± 0.07 mm and 0.28 ± 0.03 mm, respectively. The maggot passed through three distinct instars and average duration of each instar was 0.81 ± 0.14, 1.60 ± 0.40 and 2.61 ± 0.29 days, respectively. The total maggot period was on an average 5.02 ± 0.83 days. The average length and width of first instar maggot was 1.52 ± 0.20 mm and 0.31 ± 0.05 mm. The average length and width of second instar maggot was 6.26 ± 0.78 mm and 1.23 ± 0.06 mm. The average length and width of third instar maggot was 9.56 ± 0.66 mm and 2.19 ± 0.22 mm. The prepupal and pupal period had an average of 0.77 ± 0.42 and 8.55 ± 0.31 days, respectively. The total pupal period was an average of 9.32 ± 0.73 days. The average length and width of prepupa was 5.68 ± 0.11 mm and 2.57 ± 0.05 mm and pupal length and width was 5.68 ± 0.11 mm and 2.57 ± 0.05mm, respectively. The male and female fruit fly lived for an average of 27.7 ± 1.42 days and 34.12 ± 1.50 days, respectively. The average length and width of the male fruit fly 8.18 ± 1.70 mm and 11.16 ± 5.70 mm whereas the female fruit fly measured 9.34 ± 1.90 mm and 15.43 ± 3.24 mm, respectively. The pre-oviposition and oviposition periods was varied an average of 12.56 ± 1.62 and 21.44 ± 4.89 days, respectively. Fecundity of female of B. cucurbitae was an average of 74.84 ± 11.69 at 16.8ºC to 32.6ºC temperature (Av. 27.62 ± 4.60ºC) and 60.6 to 90.5 per cent relative humidity (Av. 80.18 ± 5.85 % RH). Sex ratio of male and female B. cucurbitae at 16.8ºC to 32.6ºC temperature (Av. 27.62 ºC ± 4.60ºC) and relative humidity 60.6 to 90.5 per cent (Av. 80.18 ± 5.85 % RH) was 1: 1.12. The entire life span of male was an average of 21.92 ± 5.83 days and that of female was an average of 25.28 ± 5.96 days. Thus, the life span of male was shorter than female.