| Offences Under the Penal Code of Ceylon | G.L. | Peiris | 1973 | General |
| Official Ceylon Handbook, The - British Empire Exhibition 1924 | N/A | N/A | 1924 | General |
| Official Language Bill - Parliamentary Debates - Official Report | Government of Sri Lanka | Hansard | 1956 | Politics |
| Official Souvenir, MCC Test Team to Australia, Board of Control for Cricket, Ceylon | R. B. | Wijesinha | 1965 | General |
| Oh No Crow | Joanna | Perry | 2021 | General |
| Olcott's Contribution to the Buddhist Renaissance | Saddamangala, Dr | Karunaratne | 1980 | Religion |
| Old Sinhalese Nursery Rhymes & Songs | Heather | Hamer | 1999 | General |
| Olwyn's Beach Wadiya, Internationally Renowned Sea Food Restaurant | H. M. Mervyn P. | Herath | 2004 | General |
| On A London Times Editorial On The Sri Lankan Problem | QASLU | N/A | 1986 | General |
| On Demonology & Witchcraft in Ceylon | Dandris | De Silva Gooneratne | 1998 | Religion |
| On Demonology and Witchcraft in Ceylon | Dandris | De Silva Gooneratne | 1998 | General |
| On Horseshoe Street | Tissa | Devendra | 2005 | Literature |
| On The Beach - Fishermen, Fishwives & Fishtraders in Lanka | R.L. | Stirrat | 1988 | General |
| On The Chronicles of Ceylon | B.C. | Law | 1994 | History |
| On The Development of Sinhala Cinema (1947-1967) | Ranee | Savarimutthu | 1977 | General |
| On The Path To Untimate Reality | Kandiah | Somasuntharam | N/A | Religion |
| On The Track of Unknown Animals | Bernard | Heuvelmans | 1965 | General |
| On The Wings of Thoughts - Excerpts of Speeches, Hon R. Premadasa | N/A | N/A | 1978 | Politics |
| On The Xtra-Judicial Xecution of Richardoysa | Batty | Weerakoon | 1990 | General |
| Once Upon A Tender Time | Carl | Muller | 1995 | Literature |
|
|
