Protein intake is essential for maintaining muscle mass, strength, and physical performance in older adults, and both the quantity and quality of protein play critical roles. But not all proteins are equal - differences in amino acid profiles and digestibility between plant and animal sources may influence their effectiveness in supporting muscle health. Therefore, understanding the impact of protein quality and source type is crucial for developing dietary strategies that optimize musculoskeletal outcomes in aging populations. The aim was to investigate associations between protein intake, sources, and quality with muscle mass, strength, and function in older Australian adults. Cross sectional data from 154 participants aged 65 years and over from the Senior’s Thinking, Exercise, Protein, Study (STEPS) randomized controlled trial were used. Dietary data (two 24-hour food diaries) was used to derive total protein intake (g/day), as well as protein intake from either animal or plant-based sources (g/day). Protein quality per meal was derived using the alpha tool (1) and expressed as a meal protein quality score ranging from 0-100, with a score of 100 being the highest protein quality. Muscle mass was measured using dual-energy X-ray absorptiometry (DEXA), muscle strength was assessed using a 3-repetition maximum (3-RM) leg press test and an isometric knee extensor strength (KES) (kg). Muscle function was measured using the Timed Up-and-Go (TUG) test, Four-Square Step Test (FSST), and the 30-second Sit-to-Stand (STS) test. Of the 154 participants, 62.34% (n = 96) were female, there was a mean age of 70.73 (SD 4.13), and almost half of participants had completed tertiary education (n = 72, 46.75%). There was an average intake of 91.08 (SD 26.33) g/day of protein, and 1.24 (SD 0.43) g/day of protein per kilogram of bodyweight. Protein quality scores (daily and per main meal) will be assessed. Crude and adjusted regression models will be run to examine the relationship between dietary protein intake (total, plant/animal) and muscle mass, strength and function. The findings from this study will provide insight into the associations between protein source and quality, and muscle mass, strength and function. This information is essential for supporting muscle health and functional capacity in ageing populations.