Since its discovery in 2005, human bocavirus 1 (HBoV1) has globally been one of the most common respiratory viruses. It is currently accepted that HBoV1 is a pathogen, causing upper and lower respiratory tract infections (LRTIs) in children. However, due to the prolonged HBoV1 DNA shedding from the upper airways and the subsequent high rate of co-detections with other respiratory viruses, the interpretation of positive polymerase chain reaction results is challenging. The aim of this study was to identify acute HBoV1 infections by the presence of HBoV1-specific IgM and IgG measured by competition enzyme immunoassay, to elucidate the induction of Th1/Th2 cytokines, and to describe the clinical characteristics associated with acute HBoV1 infection in hospitalised children less than five years of age with LRTI. HBoV1 IgM was detected in 19/102 (18.6%) and IgG in 66/102 (64.7%) patients. HBoV1 IgM was most frequently found in patients aged 13 to 24 months. Pneumonia and acute wheezing were the most common clinical diagnoses among HBoV1 IgM positive patients. The seroprevalence of HBoV1-specific IgG increased with age, reaching 85% by the age of five years. INF-γ, IL-4, IL-5, and IL-10 were observed to be higher in patients with acute HBoV1 infection.