It depends. While the regulations do allow rollover of assets between 401(k) plans and 403(b) plans, employers are not required to allow rollovers into the plans they maintain. Consequently, the receiving plan (or employer that sponsors/maintains the plan) ultimately decides if it will accept rollover contributions from a 401(k) or other plan. Check with your employer or 403(b) provider to determine if the 403(b) in which you participate allows for rollovers from 401(k) plans.
If the 403(b) does not allow for rollovers, and you are required to distribute the assets from the 401(k) plan because you separate from service with your former employer, you may consider rolling the assets to a Traditional IRA.
This question was answered by Denise Appleby