Nigeria relatively lacks contemporary requirements of ESM as most sports administractors function on trial and error basis leading to poor performances in sporting festivals and other sporting events. However, reports have shown that South-west zone is not doing well in major competitions which may be an indication of poor ESM by sport administrators. Previous studies focused mainly on managerial capabilities with little consideration on organisational structure. This study therefore, was designed to investigate Organisational Structure (OS):-formalisation, centralisation, complexity as predictor of effective sports management among sports administrators in the South-west, Nigeria.The study was anchored on Organisational Theory and descriptive research design of correlation type was adopted. Multistage sampling procedure was used. Purposive sampling technique was used to select staff of the state Sports Councils and Ministries of Youth and Sports who are in the managerial cadre. Total enumeration technique was adopted to select all the managerial cadre staff in sport council and Ministry of Sports. One thousand and thirty four sports administrators in South-west were enumerated. The instruments used were Formalisation (r=0.71), Centralisation (r=0.73), Complexity (r=0.70) and ESM (r=0.74) scales. Data were analysed with Pearson product moment correlation, Analysis of variance and Multiple regression at 0.05 level of significance. The respondents’ age was 37.60±2.30 years and 76.7% were male. There was a significant difference in sports participation based on states (F(5;1028)= 18.57). Lagos (x =20.30) performed best, followed by Ogun (x =17.91), Oyo (x =17.22), Ondo(x =16.73), Osun (x =15.30) and Ekiti (
x =13.87). Formalisation (r=0.04), centralisation (r=0.76) and complexity (r=0.65) correlated with ESM. There was a significant joint contribution of OS (F(3;1030)= 528.527, p<0.05, Adj. R2=0.605) on ESM, accounting for 60.5% of its variance. Centralisation (β=0.60) and complexity (β=0.24), contributed significantly to ESM, while formalisation did not. Centralisation and complexity influenced effective sports management in the South-west, Nigeria. The authorities of the Ministries of Youth and Sports as well as Sports’ Councils / Commissions in South-West, Nigeriashould should intensify efforts to educate their staff on the need to imbibe organisational structure for effective management of sports.