Plant protein hydrolysate are a rich source of peptides and other bioactive substances which is the reason why scientific research examines their effect on the maintenance and growth of cultured cells. This experiment examines the effect of flaxseed protein hydrolysate on the viability and differentiation of muscle cell C2C12. It was also tested whether the hydrolysate has protective effect on C2C12 atrophy induced by dexamethasone treatment. C2C12 cells were treated with flaxseed protein hydrolysate in concentration range of 0,5 – 5 mg/mL and viability was determined after 48 h. In order to determinate protective effect of flaxseed protein hydrolysate, the cells were treated with 1 mg/mL hydrolysate and its effect on differentiation of muscle cells was monitored over seven days. Protective effect of 1 mg/mL hydrolysate on C2C12 cell atrophy induced by dexamethasone treatment was monitored for two days. The number of cells was determined by Trypan blue method, viability of cells was determined by MTS method, and the effect on differentiation was determined by measuring diameter with program Digicyte and by staining cells with crystal - violet. Based on the obtained results, the inhibiting effect of flaxseed protein hydrolysate on viability of cells is visible in range of 7,89 - 17,37 %. The results also showed a 10 % reduction in the diameter of differentiated myotubes treated with the hydrolysate. By observing the morphology of untreated and treated cells with 1 mg/ml hydrolysate, it was noticed that treated cells cover a smaller area for growth and form a round clusters in relation to untreated cells. In adition, a mild protective effect of flaxseed hydrolysate was observed (+6,5 %) on C2C12 cells atrophy compared to cells treated only with 100 μM dexamethasone.