Durian (Durio zibethinus Murr.) is regarded as 'king of the fruits' in Thailand and its export value tops the list of Thai fruits. However, no plant and soil testing methods are used for durian fertilization even though durian is heavily fertilized due to its high value in both domestic and oversea markets. This paper presents recent research on the development of leaf nutrient diagnosis standards for durian. The standardized sampling method recommended for durian is to select the third or fourth leaf on terminated flush when they are 5-7 months old. The leaf diagnosis established for durian leaves are 20-24 g kg-1 N, 1.5-2.5 g kg-1 P, 15-25 g kg-1 K, 17-25 g kg-1 Ca, 2.5-5.0 g kg-1 Mg, 40-150 mg kg-1 Fe, 50-120 mg kg-1 Mn, 10-25 mg kg-1 Cu, 10-30 mg kg-1 Zn and 30-70 mg kg-1 B. The leaf nutrient standards were the same for all durian varieties. Sixty to eighty leaves were sampled from 15-20 durian trees from each orchard for diagnosis. These leaf analysis criteria were used as the basis for fertilizer recommendations. After 6 years in the service, 1,120 durian leaf samples were analyzed. According to the diagnostic criteria, the major nutritional problems of durian in Eastern Thailand are low levels of N, K, Ca, Fe and B. For the soil, it was found that more than 90% of the soils had pH less than 5.5. These soils were low in K, Ca and Mg. In contrast, more than half of the soil samples contained higher than 60 mg P kg-1 which was the result of P accumulation.