An experiment was conducted to determine the effect of mannanoligosaccharide, yucca extract, β-glucan and organic acid on growth performance, nutrients digestibility and amino acid digestibility in pigs weaned at 21 days of age. One hundred and eighty piglets (5.82 ㎏ average body weight, average 28 d of age) weaned at 21 days old were assigned to six treatments, which were Antifree group (basal diet), Anti group (basal diet + 120 ppm chlortetracycline, CTC-125^ⓡ, JEIL VET. CHEM. Co. Ltd.), MOS group (basal diet + 0.2% mannanoligosaccharide, BIO-MOS^ⓡ, Alltech Inc.), YE group (basal diet + 0.012% yucca extract, Fibergest^ⓡ, P. S. F Organic Inc.), GLC group (basal diet + 0.2% β-glucan, Macrogard^ⓡ, Biomaczymal Co.) and CAL group (basal + 1% organic acid, Calprona-P^ⓡ, Verdugt B. V.). Each treatment has 6 replicates with 5 piglets in each replicate. During day 0∼14, there were no significant differences in ADG, ADFI and FCR among treatments. During day 15∼42, there were no significant differences in ADF and ADFI among treatments. In this period, Antifree group showed higher (P$lt;0.05) FCR compared with CAL group. Overall, there were no significant differences in ADG and ADFI. In addition, Antifree group showed lower (P$lt;0.05) FCR compared with GLC and CAL groups (P$lt;0.05). There were no significant differences in all nutrients digestibility, essential and non-essential amino acids digestibility among treatments. Total feed cost was lower in YE group compared with GLC group (P$lt;0.05). GLC group showed higher (P$lt;0.05) total feed cost per total weight gain compared with other treatments except CAL group.