Abstract: This laboratory experiment was carried out at the Department of Agricultural Technology, Mahasarakham University, Northeast Thailand during June to October 2007. The experiment aimed to search for the most appropriate harvesting age of fruits of Santol orchard plants with respect to colour, tissue texture, total soluble solid content, titratable acidity and pH of Santol fruits. A Randomised Complete Block Design (RCBD) with four replications was used. Each replication consisted of 10 fruits, thus a total of 160 fruits were used. The Santol fruits were harvested at different ages, i.e., 100, 115, 130 and 145 days after full bloom of flowers and these harvested ages were used as treatments, i.e., 100 for T1 (Control), 115 for T2, 130 for T3 and 145 for T4. The results showed that the most appropriate harvesting date for high quality Santol fruits was found with T4, i.e., 145 days after full bloom of flowers where Santol fruits of T4 gave the highest mean values of fruit length, diameter, fresh weight fruit-1 of 10.71 cm, 9.31 cm and 399.76 g, respectively. Yellowness of skin colour of fruits was evenly distributed. Total soluble solid content of pericarp, flesh tissue and seeds were highest for T4 with mean values of 13.93, 15.05 and 18.260 brix, respectively. Flesh texture density highly decreased with an increase in numbers of days after full bloom of flowers. Titratable acidity content in fruits was highly decreased with an increase in numbers of days after full bloom of flowers whereas a reverse was found with pH of fruit juices.