Eighteen suckling buffalo calves were divided depending on weight and sex into three similar experimental treatments (4 males and 2 females per each) to study the effect of mannan oligosaccarides (MOS) or commercial probiotic supplementation on performance, some blood constituents and economic efficiency of suckling buffalo calves. The calves of the 1^st  treatment (R1) were fed a basal ration consisting of whole milk, starter and berseem hay. The calves of the 2^nd (R2) and 3^rd treatments (R3) were fed a basal ration supplemented with either 6 gm probiotic or 4 gm MOS per calf per day, respectively. Supplementations were mixed with whole milk once a day during morning suckling. Calves were individually fed milk from 3^rd days old, while solid feeds (starter and berseem hay) were  fed ad libitum in groups starting from 2^nd week of age up to weaning at 15^th weeks of age. Water was available free choice. Feed intake was measured daily, cases of diarrhea or any other diseases were recorded. Animal body weights were recorded biweekly. Three digestibility trials were carried out at 10^th week old to evaluate the tested treatments. Blood sampling were conducted at days 35,70 and 105. The results obtained were: The best digestibilties of various nutrients were recorded with calves fed R3 followed by those fed R2. Calves fed R3 had the highest values of average daily feed intake expressed as DM, TDN and DCP, while calves fed R1 recorded the lowest intake. The averages of daily body gain were 0.660; 0.722 and 0.779 kg/ head/ day for calves fed R1, R2 and R3, respectively. The MOS and probiotic supplementation for claves induced increases in serum concentrations of total protein, albumin, globulin, AST, total lipids, glucose, Zn and Fe than control calves. However, depressions in serum concentrations of ALT, cholesterol, triglycerides, and  urea-N were detected. There were significant (P<0.05) differences  in serum  total protein,  albumin,  AST, ALT, total lipids, cholesterol , glucose, urea-N, Zinc and Fe concentrations among the age of claves. Calves fed R3 had the best feed conversion as kg DM, TDN and DCP/ kg gain, while calves fed R1 showed the poorest feed conversion. Calves fed ration supplemented with MOS and probiotic recorded lowest diarrhea cases. Less daily cost/ kg gain was recorded for calves fed either R2 or R3, while the highest expensive kg gain cost was with those fed R1. It can be concluded that, supplementing milk of suckling buffalo calves with mannan oligosaccarides (MOS) or commercial probiotic product enhance feed intak, body weight gain, feed conversion, some blood parameters and rearing economic efficiency, with a higher superiority of MOS results.