Original scientific paperIn this study, a quaternary biocompatible shape memory alloy (BSMA) was produced by adding different ratios of Ta and V elements to the equiatomic NiTi and Ni27Ti50Nb23 ternary alloy. Prepared alloys; They were coded as Ni50Ti50 (EB1), Ni27Ti50Nb23 (EB2), Ni27Ti50Nb22Ta1 (E1), Ni27Ti50Nb20Ta3 (E3), Ni27Ti50Nb18Ta5 (E5), Ni27Ti50Nb22V1 (B1), Ni27Ti50Nb21V2 (B2) ve Ni27Ti50Nb18V5 (B5). The BSMA samples prepared to be used for this experiment were cut in regular and equal sizes and subjected to sterilization processes. Simulated body fluid (SBF), in which the prepared alloys were in contact, was prepared in the laboratory and used in in-vitro studies. In this study, a closed incubator system was preferred and a pathogenic bacterium, Pseudomonas aeruginosa (ATCC 27853), was used. For the production of bacteria, Nutrient agar solid was prepared. Bacterial cell density grown in the artificial body fluid with the control (simulated body fluid); determined for each alloy using a spectrophotometer (OD600). In the other stage; bacteria were cultivated from liquid culture (SBF containing Pseudomonas aeruginosa) to petri dishes containing solid media by smear method for each alloy. At the end of this period, bacterial colonies were observed with an ultraviolet (UV) lamp. The degree of biocompatibility was evaluated according to the results of the cell culture test performed for examination. It was observed that the cell density values of NiTiNbTa BSMAs added with Ta element were lower than the control (SBF). In addition, much lower values were determined in the alloys prepared with the increase of vanadium element contribution in NiTiNbV BSMA. According to the bacterial growth tests obtained, it can be said that the Ta element increases the biocompatibility in NiTi alloys, since fewer bacterial colonies are seen in the Ta element added environments than the others.