To improve the creep resistance is one of the key issues for the design of high temperature titanium alloys. In general, the alloying atoms diffusing slow in the alloy increase the creep resistance whereas the fast diffusers degrade it. Therefore, understanding the diffusion of alloying atoms in titanium alloys is crucial for the development of novel high temperature titanium alloys. In the present work, the diffusion of various alloying atoms in titanium under both interstitial and vacancy-mediated mechanisms are investigated by using a first-principles method. It was shown that Al, Si, Sn, etc. are normal or slow diffusers in titanium whereas Fe, Co, Ni, etc. are fast diffusers. Si is identified to enhance effectively the creep resistance. The cooperation of Si and some other alloying elements such as Mo and Re may increase further the creep resistance of titanium alloys.