Laparoscopic sleeve gastrectomy (LSG) has demonstrated high long-term effectiveness and major advantages over other techniques. The objective of this study was to analyze changes in physical fitness parameters in morbidly obese patients during 6 months after LSG. We conducted a descriptive observational study with 6-month follow-up in 72 LSG patients, evaluating changes in body mass index (BMI), functional capacity (6-min walking test), hand grip strength (manual dynamometry), flexibility (fingertip-to-floor test), balance (Flamingo test), physical activity level (International Physical Activity Questionnaire, IPAQ), and perception of general physical fitness (International Fitness Scale [IFIS] questionnaire). The ANOVA revealed significant improvements in BMI, functional capacity, flexibility, balance, and physical activity level (P < 0.001) at 6 months, with an improvement in the perception of physical fitness in most cases. No significant changes were found in dominant hand (P = 0.676) or non-dominant hand (P = 0.222) dynamometry. General physical fitness was positively correlated with BMI and distance in the 6-min test, and was negatively correlated with fingertip-to-floor distance. Morbidly obese patients showed major improvements at 6 months after LSG in functional capacity, balance, mobility, and physical activity, with no change in grip strength. These improvements were related to a better self-perception of general physical fitness.