To examine the impact of acquisition time on Lutetium-177 (177Lu) single-photon emission computed tomography (SPECT) images using Monte Carlo simulation. A gamma camera simulation based on the Monte Carlo method was performed to produce SPECT images. The phantom was modeled on a NEMA IEC BODY phantom including six spheres as tumors. After the administration of 7.4GBq of 177Lu, radioactivity concentrations of the tumor/liver at 6, 24, and 72h after administration were set to 1.85/0.201, 2.12/0.156, and 1.95/0.117MBq/mL, respectively. In addition, the radioactivity concentrations of the tumor at 72h after administration varied by 1/2, 1/4, and 1/8 when comparison was made. Acquisition times examined were 1.2, 1.5, 2, 3, 6, and 12min. To assess the impact of collimators, SPECT data acquired at 72h after the administration using six collimators of low-energy high-resolution (LEHR), extended low-energy general-purpose (ELEGP), medium-energy, and general-purpose (MEGP-1, MEGP-2, and MEGP-3) and high-energy general-purpose (HEGP) were examined. After prefiltering using a Butterworth filter, projection images were reconstructed using ordered subset expectation maximization. The detected photons were classified into direct rays, scattered rays, penetrating rays, and characteristic X-rays from lead. The image quality was evaluated through visual assessment, and physical assessment of contrast recovery coefficient (CRC) and contrast-to-noise ratio (CNR). In this study, the CNR threshold for detectability was assumed to be 5.0. To compare collimators, the highest sensitivity was observed with ELEGP, followed by LEHR and MEGP-1. The highest ratio of direct ray was also observed in ELEGP followed by MEGP-1. In comparison of the radioactivity concentration ratios of tumor/liver, CRC and CNR were significantly decreased with smaller radioactivity concentration ratios. This effect was greater with larger spheres. According to the visual assessment, the acquisition time of 6, 6, and 3min or longer was required using ELEGP collimator at 6, 24, and 72h after administration, respectively. Physical assessment based on CNR and CRC also suggested that 6, 6, and 3min or longer acquisition time was necessary at 6, 24, and 72h after administration. 177Lu-SPECT images generated via the Monte Carlo simulation suggested that the recommended acquisition time was 6min or longer at 6 and 24h and 3min or longer at 72h after administration.