You might be able to lose weight that way, depending on the duration and intensity of your walking and what your diet's like. A combination of physical activity and dietary changes that include eating fewer calories seems to promote weight loss more effectively than does exercise alone.
Physical activity, such as walking, is important for weight control because it helps you burn calories. If you add 30 minutes of brisk walking to your daily routine, you could burn about 150 more calories a day. Of course, the more you walk and the quicker your pace, the more calories you'll burn.
However, balance is important. Overdoing it can increase your risk of soreness, injury and burnout. If you're new to regular exercise and physical activity, you may need to start out with short walks or walking at a light intensity, and gradually build up to longer walks or more moderate or vigorous intensity.
Once you've lost weight, exercise is even more important — it's what helps keep the weight off. In fact, studies show that people who maintain their weight loss over the long term get regular physical activity.
So keep walking, but make sure you also eat a healthy diet.