This study was conducted on "Langra Cv." mango trees growing in a private orchard, Tema, Sohag governorate. The residual effect of paclobutrazol (PBZ) was investigated on "Langra Cv." mango during the "On" and "Off" years (2011 and 2012) after its application in October 2010 and 2011 years to regulate the alternate bearing, enhanced yield and improved fruit quality. The result showed that (PBZ) application at 30 or 40 gm / tree as a soil drench reduced the vegetative growth however; it induced the early flowering and yield in comparison with alternate bearing. Also, it increased the fruit weight and yield as well as improved the fruit quality in both "On" and "Off" years.  In addition, this treatment leads to increasing the number of panicles per tree, number of hermaphrodite flowers per panicle, number of fruits per panicle and number of remaining fruits per tree in comparison with control trees on "Off " year during the two seasons of study. However, application of (PBZ) had no effect on seed weight %, pulp/seed ratio, acidity % and V.C traits in both "On" and "Off" years. Therefore, the study recommends that treating of "Langra Cv." mango trees in both "On" or "Off" years by (PBZ) at 30 or 40 gm / tree is effective for reducing the alternate bearing and improving the yield and fruit quality.