The present study was carried out under laboratory conditions to investigate the influence of four constant temperatures (20, 25, 30 and 35^oC) and 60±5% R.H.on the development of the immature stages of Phenacoccus parvus Morrison as well as on the reproductive potential of the adult, and to estimate the relation between thermal units required for the development and degree-days (DD's). The incubation period lasted 6.6 ± 0.22, 5.8 ± 0.13, 4.2 ± 0.20 and 3.2± 0.13 days for eggs at constant temperatures 20, 25, 30 and 35^oC, respectively. The developmental period of nymphal stage tended to be shortened with the corresponding increments of temperature. At a specific temperature, the  developmental period of the nymphal stage was 25± 0.09, 22.5± 0.06, 17.1± 0.12 and 13.7± 0.09 days at 20, 25, 30 and 35^oC, respectively. The calculated developmental thresholds (t₀) of the egg and nymphal stages were found to be 7.58 and 3.72^oC, respectively; meanwhile, the calculated developmental threshold of the whole immature stages was estimated as 5.71 and 5.76^oC for male and female, respectively. The mean thermal units required for development of P. parvus eggs and nymphal stages were 469.80, 134.88 DD's degree-days, respectively.