You can download Olympiad past papers by visiting web sites of Olympiad sites. Links are given here.
Biology Olympiad 2013 Marking Scheme
2011 Sri Lankan Biology Olympiad Examination
Sinhala medium Part A and Part B
Tamil Medium Part A and Part B
English Medium Part A and Part B
Marking Scheme
2010 Sri Lankan Biology Olympiad Examination
Sinhala medium | Tamil Medium Part A Part B| English Medium | Marking Scheme
Answer Sheets Sinhala | Tamil | English
2009 Sri Lankan Biology Olympiad Examination
Sinhala medium | Tamil Medium | Marking Scheme
Model questions for 2009 Sri Lankan Olympiad
English medium | Sinhala medium | Tamil medium