Tomato is one of the most widely grown vegetables in Ethiopia, particularly in Northwest Ethiopia. Tomatoes suffer a high amount of postharvest losses along the postharvest supply chain due to its climacteric and perishable nature. There are very limited studies regarding the causes and extent of postharvest losses of tomato in Northwest Ethiopia. The aim of the present study was to assess the quantitative and qualitative postharvest loss of tomatoes along the postharvest supply chain in Northwest Ethiopia. The study was conducted in tomato fruits produced in three productive kebeles (Chimba, Gumara, and Kudmi) of Northwest Ethiopia following FAO (2014) load tracking method. The experiment was conducted with two factors arranged in a randomized complete block design. The first factor: growing location consists of three levels (Chimba, Gumara, and Kudmi) and the second factor: postharvest supply chain consists of four levels (Farm, Transportation, Wholesale, and Retail) with a total of four replications. Key informant interviews were conducted to document common pre-harvest and postharvest handling practices of tomato in the study kebeles. Quantitative postharvest loss, environmental condition (temperature and relative humidity) and changes in produce quality (weight loss, color, firmness, titratable acidity, total soluble solids, pH, sugar-acid ratio, and ascorbic acid) were determined. Data were analyzed using SAS software version 9.2. Postharvest losses of tomatoes on average ranged from 6.17-8.62%, 1.23-8.24%, 3.35-4.30%, and 9.38-12.58% at the farm, transportation, wholesale, and retail levels, respectively. The average total postharvest losses of tomatoes among three locations were 25.91±1.04% along the postharvest supply chain. Results indicated that firmness, fruit color (L* and b*), titratable acidity, and ascorbic acid leads to a significant decrease from farm to retail levels. However, physiological weight loss, fruit color (a* and a*/b*), pH, total soluble solids, and sugar-acid ratio was significantly increased from farm to retail levels due to ripening of tomatoes and weight loss through transpiration. The result shows that the storage and handling of tomatoes at ambient temperature and low relative humidity was a significant effect on the quantitative and qualitative postharvest losses of tomatoes with increased storage time along the postharvest supply chain. Besides, inadequate pre-harvest management, inappropriate harvesting time and method, lack of appropriate harvesting containers, lack of on-farm storage facilities, lack of appropriate packaging materials, poor road access and infrastructures, inappropriate mode of transport, lack of storage facilities at wholesale and retail levels, and lack of reliable market system and market information were also identified as contributors for the high postharvest losses of tomatoes observed in present study. Their cumulative effects lead to immediate physical, physiological, and chemical losses of tomato which results in decay, bruising, mechanical damage, and quality loss in present study. The information from this study could be used as a basis to minimize the postharvest losses of tomato, by policymakers to put appropriate policies to minimize postharvest losses along the supply chain of perishable crops and by postharvest experts to give the appropriate advice for different actors in the supply chain of tomato.