The population dynamics of black parlatoria scale, Parlatoria ziziphi (Lucas) (Hemiptera: Diaspididae) were studied on sour orange (citrus aurantum) for two successive years (2005-2006) at Qalubyia Governorate. The obtained results revealed that P. ziziphi had three generation a year. The highest generation occurred in summer followed by moderate generation in autumn and relatively smaller generation in winter. The summer generation peaked in early June and started from mid March or early April until mid July with duration of 3.5 - 4.5 months; the autumn generation peaked in early October and extended from mid July or early August to late December with duration of 5 – 5.5 months whereas the winter generation peaked in mid January and started from early January to early April and lasted for 3 months.  The main weather factors (daily mean max. and min. temperatures and % R.H.) affected greatly on the annual generations of P. ziziphi in both studied years. The summer generation affected with 51 - 52% , while autumn and winter generations affected  with  47 - 63.4% and 93.5 - 94.8%  respectively.