The effect of oxygen content on aging behavior and invar characteristics of Ti-29Nb-13Ta-4.6Zr (TNTZ) were investigated. The age hardening of TNTZ aged at 573 K and 723 K is enhanced with the oxygen content. The ω phase precipitates and grows from early stage of aging in TNTZ regardless of the oxygen content when aged at 573 K. The lath-like shape α phase precipitated in TNTZ aged at 723 K increases in size with the oxygen content. The elastic modulus increases with the oxygen content and aging. The ω phase increase the elastic modulus to a greater extent than the increase due to the α phase. The tensile strength increases with the oxygen content and aging, while the elongation decreases. TNTZ with oxygen content of 0.1 mass% exhibits invar-like characteristics through severe cold working. A higher oxygen content suppresses the invar-like characteristics of TNTZ.