Adenotonsillectomy is the most common surgical treatment in children. Acoustics analysis of speech and voice and nasometric studies are important phoniatrician role, they are additional instrumental measures in voice and nasalance assessment. The effects of adenotonsillectomy on both speech and voice are assessed by subjective methods and instrumentally by computerized speech lab (CSL) main program for evaluation of supralaryngeal characteristics (formants frequencies F1,F2,F3) .Multidimensional voice program (MDVP) used for (Fo, Jitt%, shimmer dB, N/H) and Nasometer 6200 for nasalance score for nasal sentence ,oral sentence, /m/ and /n/ sounds. The parameters were measured one week preoperatively, and one month postoperatively. The results shows improvement in voice quality as (FO, Jitt%, shimmer dB, N/H) are decreased significantly postoperatively. The nasalance scores for /m/, /n/ sounds and nasal sentence are significantly increased post operatively which became near normal that indicates improvement of resonance. This thesis concluded that adenotonsillectomy can improve voice quality and improve resonance if well done especially with preoperative assessment to prevent complications related to resonance and if happened follow up after 3 months should be done before rehabilitation or surgical intervention to correct the complications.