When a CEO resigns, what kind of change in organizational behavior are required?

Hi Trang:
In most of the case, the only thing is required to change is ... the CEO position obviously. As there is no need to change a good business even after there is a change in CEO (or any) position.
However, if the company is currently in poor business situation (and the CEO is responsible for), then changing the CEO will be a good opportunity for the company to make significant (positive) change in any area the Board think it is necessary: Corporate Strategy, Business Strategy, Operation, Management, Staff, etc.

It will be very much different, if your question is: What and How to manage changes when a CEO resigns. It is a very good (and challenging) question for businesses if that is a good CEO.

CEO change is a big changes compared to other organizational change. Usually there can be 2 cases:
1. CEO is fired by the Board because of low performance: In this case, the organization should be put in the alarm mode too. (cause though the CEO is responsible for the whole organization bad performance, the bad results also caused by the organization itself too). Hence the most important behavior required is each department would review their own performance ; honestly take responsibility to find where the unsatisfying results is and make the plan to work hard to improve
2. CEO is ending his term and the Board has find the new CEO: This case is much more positive compared to the other. New CEO come may bring with him new working style, new culture and even some new team member. Key Organization behavior required is OPENNESS. Don't stick to they old way of the old CEO, don;t compare and complain, accept that any change is for better and extend the organization comfort zone to achieve better growth.

When a CEO is also the face of the company, like Steve Jobs, there will always be a knee jerk reaction to his/her resignation because the future of the company and/or its continued success is an unknown. The CEO normally does not operate in a vacuum and to create a successful company has surrounded himself with great people. The problem is that the perception may be that the success and innovation within the company all comes from the CEO. In the case of Steve Jobs, the perception is even more pronounced because Apple brought him back to turn the company around and he did. If the culture of innovation and valuing the contributions of all employees is maintained then Apple has a good chance of continuing its success. Only if the company has been run by a martinet who does not value employees, their contributions and does not create a culture of innovation, should it change its behavior. We have also seen the opposite where a CEO has resigned and the stock has risen because the perception is that anyone is better than the person who resigned.

Change is inevitable when the CEO changes. Each individual brings their own values, style and business biases to the job and CEO's typically set the cultural tone of the organization.
If the former CEO was well liked, expect some resistance to the new leader and some foot dragging when it comes to new initiatives. If the former CEO was not particularly well liked, expect some combination of immediate hero worship and skepticism.
In any case, the new person must be an excellent communicator and be reasonable, fair and consistent in implementation of all things new for the first year,

Generally, whatever the new CEO wants .... Changes are generally decided by the new CEO, perhaps with some instructions from the Board and hopefully with a lot of input from the people within the organization!