Keropok lekor is a famous fish-based traditional food from Terengganu, Malaysia. Due to the progressive cultivation activity of oyster mushrooms in Malaysia and their high nutritional values, they were selected to be incorporated in keropok lekor formulations to replace a partial percentage of fish flesh. In this study, the determination of nutritional composition and physical as well as evaluation of sensory acceptability of oyster mushroom-containing keropok lekor were carried out. Three formulations of keropok lekor with different ratios of fish flesh to oyster mushroom were prepared as follows: control (100:0), sample A (75:25), and sample B (50:50). In terms of nutritional composition, the results found that the value of ash, moisture, and carbohydrate contents of keropok lekor with oyster mushroom substitutions were significantly higher (P<0.05) than control keropok lekor. However, the experimental keropok lekor (sample A and sample B) had significantly lower (P<0.05) protein and fat contents than the control sample. The highest value of hardness, springiness, cohesiveness, and chewiness of the control sample (100% fish flesh) was obtained in comparison to keropok lekor substituted with oyster mushroom. In the context of colour, the value of L* (whiteness) increased by substituting oyster mushrooms into keropok lekor formulations due to the light colour of the mushroom. The 9-point hedonic scale test indicated that consumers’ preferences for experimental keropok lekor (sample A and sample B) were significantly (P<0.05) higher scores as compared to the control sample in terms of texture, taste, and overall acceptance. In contrast, appearance, colour, and aroma attributes obtained lower scores. The findings also suggested that replacing fish flesh with oyster mushrooms in keropok lekor has great potential to be commercialized in the market and represented as a new variety of keropok lekor in the food industry.