Purpose: To assess the alteration in keratinized mucosa (KM) dimensions during the early healing period after implant placement and the influence of the variables measured during implant surgery on KM alteration. Materials and Methods: The study participants were consecutively recruited from patients who had received implants following a nonsubmerged surgical protocol. The implant had to be placed in an extraction socket that had healed for more than 6 months without any soft or hard tissue augmentation. Keratinized mucosa width (KMW), keratinized mucosa thickness (KMT), soft tissue level (STL), and probing pocket depth (PPD) were all measured at implant placement as well as at 3 and 6 months after implant surgery. The influence of these variables measured during implant surgery on the 6-month KMW alteration was assessed. Results: A total of 66 implants in 55 patients who completed the follow-up examination after 6 months were included in this study. KMW, KMT, and STL significantly decreased at the 3- and 6-month follow-ups by 0.7 to 1.2 mm. KMW decreased by 24.6%. Mesial PPD significantly increased between the 3- and 6-month follow-ups. In the multivariate generalized estimating equations (GEE) analysis, the implant diameter negatively influenced KMW alteration at the 6-month follow-up, but the KMW at implant surgery was positively influenced at the 6-month KMW alteration follow-up. Conclusions: The KMW decreased significantly at the 3- and 6- month follow-ups after implant placement. If the initial KMW was wider, the KMW decreased more at 6 months after implant placement. Therefore, it is important to carefully monitor KMW alterations during the early healing period to ensure optimal esthetics and peri-implant tissue health.