The objectives of this study are to evaluate the effects of some basic factors, namely extender type, sperm volume, cryoprotectant concentration, cryopreservation and storage time, on the quality of Mekong giant catfish (MGC) sperm. The following results are obtained from conducted experiments. The sperm kept in Hanks balanced salt solution (HBSS) extender consistently produced good results in terms of motility. The highest motility grade (4.0) was observed after 12 hours of examination and still a very satisfactory grade (3.3) was observed after 48 hours. The percentage of live cells of the sperm kept in HBSS was also highest (45.3%). The optimal amount of cryoprotectant (DMSO) prior to cryopreservation was 8%, which gave the best motility grade (4.0) up to the first 72 hours of observation while at 120 hours the motility grade was 3.3. The fertilisation rate of MGC fresh sperm in HBSS (2 ml) and 1 gram eggs was 47.1% while that of cryopreserved sperm under the same conditions was 36.2%. When crossed with P. hypophthalmus, the fertilisation rates of a 2-week- and a 1-year-cryopreserved sperm sample were 36.2% and 30.9% respectively.