Senior Executive Service Improvements Act

Senior Executive Service Improvements Act - Amends the Civil Service Reform Act of 1978 to provide that the initial rate of pay of a Federal employee in the Civil Service who has at least five years of continuous service and is appointed to the Senior Executive Service (SES) as a career appointee, or who holds a position which is converted to a career reserved position in the SES, shall not be less than that individual's basic pay rate before such appointment or conversion.

Revises the limitations on reassignment of career appointees within the SES to: (1) provide that such appointees may not be involuntarily reassigned within 120 days after appointment of a new immediate noncareer supervisor who has responsibility for evaluating their performance; and (2) exclude up to 60 days of such a career appointee's detail or temporary assignment apart from his or her regular position from the 120-day period following the appointment of a new agency head or immediate supervisor within which the appointee may not be involuntarily reassigned.

Requires the Office of Personnel Management, in order to promote the professional development of career appointees, to encourage them to take advantage of opportunities for sabbaticals, training, or details to other agencies, State or local governments, or the private sector.

Grants the Merit Systems Protection Board the authority to mitigate adverse actions against SES members in the same manner as provided for other Federal employees in the Civil Service.