To explore the clinical features and pathogenic characterization of the obviously increasing paediatric cases caused by nontyphoidal Salmonella (NTS) in recent years, the present study retrospectively analyzed the clinical features, distribution of serovars, and antimicrobial resistance of NTS in the infected children in Jinshan Hospital of Fudan University between January 2018 and December 2021. The difference in these features between before and after the Corona Virus Disease 2019 (COVID-19) epidemic was also analyzed. The average isolation rate of NTS in paediatric diarrhea cases was 18.1% (110/609), with the rate significantly higher in 2020-2021 (after the beginning of COVID-19) (21.3%，57/268) than in 2018-2019 (15.5%, 53/341, P＝ 0.04). NTS-infected cases were more frequent in the age group of 6 months to 3 years old (80.0%, 88/110), peaking from May to October (84.5%, 93/110). The common clinical symptoms included fever (70.9%) and blood-in-stool (22.7%). The children with NTS infections were administrated with the third-generation cephalosporins, and the therapy mostly lasted for five to seven days. All the cases recovered. The NTS isolates represented 21 serovars, with monophasic variant of S. Typhimurium the commonest (29.1%, 32/110), followed by S. Typhimurium (26.4%, 29/110). Antimicrobial susceptibility testing showed that the resistance rate of NTS isolates to ceftriaxone was 21.8%, while the resistance rates to azithromycin and ciprofloxacin were both very low (8.2% and 6.4%, respectively). 29.1% of the NTS isolates were multidrug-resistant, while 2.7% were resistant to all the tested antibiotics. NTS has become an important pathogen responsible for bacterial inflammatory diarrhea in the children residing in and around Jinshan District of Shanghai. The prevalence of NTS infections is increasing, which is probably associated with the increase of infections caused by S. Typhimurium and its monophasic variant. These NTS isolates show a high resistance rate to the third-generation cephalosporins which are often used in the clinical practice. Therefore, it is necessary to warrant continual surveillance on the changes of epidemiological features and antimicrobial resistance of NTS.