Observations made during the' arribadas' or mass nesting of the Olive ridley Lepidochelys olivacea during 1987 at Gahirmatha rookery, Orissa are reported. The first mass nesting occurred in a stretch of 5.7 km from 5th to 14th January and two lakhs turtles nested. During the second mass nesting in a stretch of 4.5 km from 5th to 14th March four lakhs turtles nested. Hatchlings of first mass nesting batch emerged after 60 days of incubation in March 1987 and the percentage of live hatchlings emerged from the natural nests varied from 63.25 to 98.66 (87.72). The mean carapace length in mm from 20 clutches examined varied from 40.2 to 42.8 and carapace width varied from 32.7 to 34.5. The mean weight in gm of the hatchlings varied from 14.75 to 19.10. The emergence of hatchlings of second mass nesting noticed after an interval of 50 days in May 1987 and the mean percentage of live hatchlings emerged varied from 17.95 to 90.38 (54.34). The mean carapace length in mm from 65 clutches examined varied from3 6.48 to 42.85 and the carapace width varied from 27.69 to 34.06. The mean weight of hatchlings in gm varied from 13.6 to 18.6 gm. The hatching success of first and Second mass nesting occurred in 1987 at Gahirmatha was compared and the high percentage of spoilt and unfertilized eggs and dead hatchlings was observed in second mass nesting batch.